In this study, S3 antigen of T. spiralis and T. pseudospiralis was given to the heterologous infection in albino mice. The recovered larvae were studied as regards: their number, length and steroscan examination. It was found that vaccination of mice with T. spiralis (S3) antigen induced reduction in T. pseudospiralis larval count by 66.43% and significant reduction in length. Using T. pseudospiralis (S3) antigen reduction of 74.77% in T. spiralis larval count was detected as well as significant reduction in length. Scanning electron microscopic (SEM) examination revealed more or less similar finding in both species: loss of integrity of the cuticle, some of the larvae were attacked by granulocytes mainly eosinophils and few larvae appeared completely destructed with loss of normal architecture. A peculiar finding was noticed in case of T. pseudospiralis larvae in form of fine electron dense deposits giving the cuticular surface a motling appearance.