[Objectives] A songbird may sing different songs while defending territory and attracting mates. Research shows that bird songs may have functional variation within one’s song repertoire. Light-vented Bulbul Pycnonotus sinensis, a common songbird resident in Wuhan, China, can sing 1﹣3 song types individually. Do different song types of Light-vented Bulbul have any functional differences? Do the birds change song type use between breeding season and non-breeding season? To answer these questions, we recorded songs from a Light-vented Bulbul population and explored the functional variations between the two song types (named type A and type B) which comprise the song repertoire of this bulbul population through song parameter comparisons and playback experiments. [Methods] From March to June, and October to November 2022, we recorded 1 007 songs from 15 Light-vented Bulbul territories in the campus area of China University of Geosciences, Wuhan, China. Song parameters of each song type in spring (breeding season) and in autumn (non-breeding season) were measured and compared between song types and between seasons using Wilcoxon signed-rank test. Then from April to June, and September to October 2023, we did playback experiments in the area of campus and nearby, including 18 playbacks in spring, of which 10 were for group A (song type A as playback stimuli) and 8 for group B (song type B as playback stimuli), and 11 playbacks in autumn, in which 5 for group A and 6 for group B. Behavioural parameters (number of flights, minimum distance to the speaker, time spent staying within 10 m to the speaker, number of responding songs) were measured for each playback and were compared between groups using Mann-Whitney test to explore the potential functional difference between song types, and using the Wilcoxon signed-rank test to explore the difference between seasons. [Results] Song parameters of 391 type A songs and 279 type B songs from 15 territories recorded in spring were compared and the results suggested that there were significant differences between song types in the following song parameters:peak frequency (P < 0.001), song duration (P = 0.008), peak time relative (P = 0.022), number of syllables per song (P = 0.020), number of syllable types per song (P < 0.001), energy (P = 0.042) (Table 1). Song type B has a longer song duration, more syllables, and more syllable types per song. Light-vented Bulbuls expend more energy to produce a type B song than a type A song. Songs recorded in autumn were also compared with those recorded in spring from the same territories. The results suggested the percentage of song types varies between seasons. The percentage of type A song was 52% ± 8% in spring and 62% ± 8% in autumn, while the percentage of type B song was 48% ± 8% in spring and 38% ± 8% in autumn (Fig. 3). Light-vented Bulbuls increased the use of type A song in autumn, with less usage of type B songs. Besides, the song parameters of each song type vary between seasons. Parameters with significant differences between seasons also differ between song types (Table 2). However, there were no significant differences in all responding behavioural parameters of the playback experiments in either spring or autumn between group A and group B (P > 0.05) (Table 3). Comparisons on responding behaviour parameters of Light-vented Bulbuls to the same song type playback also show no significant difference between seasons (P > 0.05) (Table 3). During spring playback, more Light-vented Bulbul individuals sang while responding and sang more songs with song type matching the playback songs than in autumn (Fig. 3). [Conclusion] It is speculated that the change in proportion of song type use between seasons may be the consequence of different singing energy allocation strategies of Light-vented Bulbuls during the breeding season and non-breeding season. Although there were significant differences in song parameters between the two song types in the repertoire of a certain Light-vented Bulbul population, no functional variations between song types were detected in this study with song playback experiments. The song-type matching during spring playbacks may be a signal of aggressive intention and Light-vented Bulbuls become less territorial during non-breeding season. This study quantified the differences in acoustic characteristics between different song types and between seasons in a population of Light-vented Bulbuls and discussed the potential functional variations between song types, which provided a new reference for understanding the communication behaviour of songbirds.