Several novel C-pseudonucleosides containing thiazolidin-4-one and phenyl connected by acetamide bond were rationally designed and easily synthesized at room temperature by using the unprotected sugar aldehyde as the starting material. The effects of the compounds on Con A-induced T cell proliferation were evaluated at five concentrations of 5, 10, 25, 50, and 100 mmol/L Interestingly,compounds 7a and 8a(n = 2, R = H) exhibited immunostimulating activities, while compounds 5a, 6a(n = 1, R = H) and 7b, 8b(n = 2, R = CH3) showed immunosuppressive activities. Another two compounds 5 b and 6b(n = 1, R = CH3) had no immunomodulating activities. These initial biological results suggested that subtle structural changes to the phenyl and acetamide bond of C-pseudonucleosides could have a significant effect on T cell proliferation bias, although it was difficult to formulate a rigorous structureactivity relationship based on the observed activities. Several novel C-pseudonucleosides containing thiazolidin-4-one and phenyl-linked by acetamide bond were rationally designed and easily synthesized at room temperature by using the unprotected sugar aldehyde as the starting material. The effects of the compounds on Con A-induced T cell proliferation were evaluated at five concentrations of 5, 10, 25, 50, and 100 mmol / L Interestingly, compounds 7a and 8a (n = 2, R = H) These two biological 5 b and 6b (n = 1, R = CH3) had no immunomodulating activities. These initial biological proposals suggest that the subtle structural changes to the phenyl and acetamide bond of C-pseudonucleosides could have a significant effect on T cell proliferation bias, although it was difficult to formulate a rigorous structure activity relationship based on the observed activities.