The anti-microbial activities of leaves and stems from Melastoma affine D. Don were studied, and the content of flavonoids and their seasonal variation were measured by means of polyamide puring and aluminium color-developing method, rutin was used as a standard. Results showed that the extract had no effects on Aspergillus flavus Link, Aspergillus niger V. Tiegh. and Penicillium chrysogenum Thom but evident inhibitive effects on Escherichia coli (Migula) Castellani et Chalmers, Bacillus subtilis (Ehrenberg) Cohn, Staphylococcus aureus Rosenbach, Proteus vulgaris Hauser and Sarcina lutea Schrōeter. The highest yield of flavonoids from leaves was 3.95% in May, which was regarded as its available component.