Gentamicin production by immobilized cells of M. echinospora has been studied in repeated-batch processes using different immobilizing carriers such as calcium-alginate, carrageenan, agar, PVA, celite, polyurethane foam and activated carbon. With ca-alginate, gentamicin production was maximum (1096 mg/l) and the bead stability was good, whereby alginate was selected for further experimentation. The role of alginate concentration, CaCl2 concentration, bead diameter, curing time and bead inoculum quantity were studied. Better gentamicin outputs (1549 mg/l) were attained with alginate 4% (w/v), CaCl2 0.2 M, bead diameter 2.69 mm, curing time 18 h and inoculum quantity 20% v/v for six repeated cycles in shake flask. Productivity of gentamicin was increased to 1.8 fold in a fluidized bed reactor with optimized alginate immobilized beads and increased reusability. The FBR was operated for 30 days in fed batch mode operation.