SW-163A and B, novel immunosuppressants, were isolated from the culture broth of Streptomyces sp. SNA15896. The molecular formulas of SW-163A and B were determined as C34H42N2O12 and C33H40N2O12 based on the HRFAB-MS analysis, respectively. Both compounds were elucidated to be a large ring ester structure through spectroscopic analyses including various NMR measurements. SW-163A and B showed immunosuppressive and antimicrobial activities in vitro.