Biotransformation of rifamycin B to rifamycin S using two strains of C. lunata namely NCIM 716 and NMU grown on various solid substrates viz., grass, paper, jowar/wheat straw, bran and bagasse was studied. Almost complete biotransformation efficiency of rifamycin B at 0. 06 mM concentration was observed within 24 hr. Among these two strains, C. lunata NMU showed 90% of biotransformation and higher rate of cellulose utilization on solid substrates vis-à-vis reference strain. Cellulase activity of both strains was also studied for exoglucanase, endoglucanase and beta-glucosidase. Column bioreactor studies with bagasse revealed further improvement in biotransformation efficiency of C. lunata NMU.