FK506 hyper-yielding mutant, called the TCM8594 strain, was made from Streptomyces tsukubaensis NRRL 18488 by mutagenesis using N-methyl-N'-nitro-N-nitrosoguanidine, ultraviolet irradiation, and FK506 sequential resistance selection. FK506 production by the TCM8594 strain improved 45.1-fold (505.4 µg/ mL) compared to that of S. tsukubaensis NRRL 18488 (11.2 µg/ mL). Among the five substrates, wheat bran was selected as the best solid substrate to produce optimum quantities of FK506 (382.7 µg/g substrate) under solid-state fermentation, and the process parameters affecting FK506 production were optimized. Maximum FK506 yield (897.4 µg/g substrate) was achieved by optimizing process parameters, such as wheat bran with 5 % (w/w) dextrin and yeast extract as additional nutrients, 70 % (v/w) initial solid substrate moisture content, initial medium pH of 7.2, 30 o C incubation temperature, inoculum level that was 10 % (v/w) of the cell mass equivalent, and a 10 day incubation. The results showed an overall 234 % increase in FK506 production after optimizing the process parameters.