Vertical transfer of maternal antibodies can provide passive protection to offspring against specific pathogens. In this study, we detected antibodies in the sera of uninfected offspring born to chronically Trichinella spiralis-infected female mice. Immunoblotting consistently revealed a distinct band at ~38 kDa in both T. spiralis excretory-secretory products and total somatic extracts. This band was identified by MALDI-TOF/TOF mass spectrometry as a cystatin-like protein of T. spiralis (Ts-CLP). Structural modeling and domain analysis indicated a typical cystatin-like fold comprising a central α-helix and an antiparallel β-sheet core. To confirm antigen identity, recombinant Ts-CLP protein was expressed and used to generate a polyclonal anti-recombinant Ts-CLP protein antibody. This antibody specifically recognized a ~38 kDa band in T. spiralis excretory-secretory products and total somatic extracts, consistent with that detected by offspring sera. Collectively, these findings demonstrate that maternal antibodies specific to Ts-CLP are vertically transferred and detectable in uninfected offspring. Although the functional significance remains to be determined, this observation provides a basis for future studies on passive immunity and host-parasite interactions.