Abstract: The length of the rectum in male Trichinella spiralis larvae is about twice that in female larvae, being 54.39(50.4-63.0) Mm in males and 28.05(18.9-31.35) Mm in females. The gonad rudiment of the female larvae has already differentiated obviously into semin-ral receptacle rudiment and uterus rudiment, while that of the male larvae remains undiffe-wntiated. The seminal receptacle rudiment is a granular, small mass and dark brown in color, while the uterus rudiment is composed of a column of several cells, and the total length of these two rudiments is 62.18 (50.4-75.6)Mm. Verifications through experimental infections proved that the length of rectum and the degree of differentiation of gonad rudiment might be used as indices to identify the sex of larvae.It was found that the sexual ratio of T. spiralis collected in Changchun was 1.82:1 (1.17-2.59:1).