Strain of Streptomyces minoensis DMCJ-144 was tried to be improved so that it produces much more the α-amylase inhibitor. Streptomyces minoensis DMCJ-144 was treated with 1 ㎎/㎖ (pH 9.0) of N-methyl-N`-nitro-N-nitrosoguanidine at 30℃ for 60 min and irradiated with UV light distanced 30 cm for 20 min. After mutagenesis, surviving colonies were cultured on the CM contaning acriflavine (10㎍/㎖) three times in order to enhance the mutability. And then through multi-level screening, colonies that α-amylase inhibitor productibility was improved were selected by modified-blue value method. After third acriflavine treatment, α-amylase inhibitory activities of selected colonies were found to be much better as compared with that of parent strain. One mutant strain showed 5.4 time inhibitory activity than the parent strain.