The karyotype of the larvae Eustrongylides ignotus, a parasitic nematode of Monopterus albus, collected from Changde City of Hunan Province was analyzed using the metaphase chromosome spread prepared from regenerative cells by an air-drying method. Results showed that the E.ignotus had a diploid chromosome number of 12 with a chromosome formula of 2n=12=10 m+2 sm, and its sex determining mechanism was the XX-XY type. There were ten autosomal biarmed chromosomes and two X chromosomes in females or one X and one Y in males. Five pairs including chromosomes 1-4, X chromosome and Y chromosome were metacentric chromosomes, while the remaining chromosome 5 was submetacentric. Every pair of chromosomes had their characteristic G-banding pattern.