T-lymphocyte (CTL) survival upon activation induced cell death is critically dependent on the expression of anti-apoptotic gene Fas apoptotic inhibitory molecule3 (FAIM3) /TOSO, which plays an important role in IL-2-mediated activation induced cell death (AICD). Down-regulation of TOSO significantly increases susceptibility to apoptosis. The present study explored the role of TOSO in regulation of calcium entry into and function of CD8 T cells. CTLs were cultured from gene trageted TOSO knockout mice (TOSO^-/-) and corresponding wildtype mice (TOSO^+/+), by stimulating with anti-CD3 for 48h followed by culturing the cells in IL2 supplemented medium for 3 days. The calcium entry upon TCR stimulation was determined by incubating with anti-CD3 followed by cross linking with secondary antibody. As a result, TOSO^-/- CTLs show significantly higher calcium entry as compared to TOSO^+/+ CTLs. Moreover, the abundance of surface marker CD44 was lower in CD4 and CD8 T cells from TOSO^-/- mice than in the respective cells from TOSO^+/+ mice. Moreover, perforin expression was significantly lower in TOSO^-/- CTLs than in TOSO^+/+ CTLs. In conclusion, TOSO is a powerful regulator of T lymphocyte of CD44 and perforin expression as well as calcium entry upon TCR stimulation.