Purple Flying Squid (Sthenoteuthis oualaniensis) is one of the most important tropical Ommatrephids, widely distributing in the tropical waters of Indo-Pacific, but little information is available on its fecundity, particularly for those populations living around South China Sea. From 28 specimens of S. oualaniensis collected in 2017 and 2018 in the South China Sea, effective fecundity and its variations with sexual maturation were assessed using bio-statistical and model fitting analysis. The specimens were measured 114﹣153 mm in mantle length, and weighed from 55.2 to 174.7 g (Table 1). The length and weight of spermatophoric sac increased with sexual maturation measured 22﹣124 mm in length and 0.03﹣3.07 g in weight, respectively (Table 2). The spermatophoric sac’s weight showed a power regression on its length. In addition, both the length and weight of spermatophoric sac were linearly correlated with mantle length and body weight (Fig. 2, 3). The effective fecundity was estimated from 1 spermatophores at stage Ⅲ to 144 spermatophores at stage Ⅶ, and the relative effective fecundity by mantle length was estimated from 0.02 to 1.62 spermatophores per millimeter. The effective fecundity increased with maturity and reached to the highest value at stage Ⅵ and remained stable till stage Ⅶ. The effective fecundity showed a linear relationship with mantle length and body weight (Fig. 4), while the relative effective fecundity by mantle length had a power regression on mantle length and body weight (Fig. 4). The spermatophore length was a power function of its weight, in which they were measured from 4.79 to 36.60 mm in length and from 0.000 2 to 0.020 0 g in weitht, respectively (Table 3). Both the length and weight of spermatophores attained their highest value at stage Ⅵ, and in addition, both of them were found linear correlation with mantle length and body weight (Fig. 6). These findings indicated that the spermatophoric sac, spermatophores and effective fecundity in the medium form of male S. oualaniensis from South China Sea showed a consistent increasing trend with sexual maturation, and significantly related to mantle length and body weight.