Quercetin is well known for its effective inhibition of cancer cell proliferation by inducing the apoptosis. In the present study, quercetin isolated from Allium cepa were loaded on a biodegradable polymer, poly(lactic-co-glycolic acid) (PLGA) microspheres and its apoptotic potential in Michigan Cancer Foundation (MCF-7) cell was investigated. PLGA microspheres before and after loading indicated no significant difference in size as the average size of the microspheres were 100 mu m. The encapsulation efficiency of quercetin on PLGA was found to be 74 +/- 1.2%. Cytotoxicity and flow cytometric analysis were used to evaluate the capacity of quercetin-PLGA microspheres (PLGAq) on anticancer activity. PLGAq were assessed at two different concentrations (1.5 mu g and 3.0 mu g) and indicated that at higher concentrations it showed effective inhibition of cancer cells. The results indicated that the PLGAq microspheres efficiently inhibit cell proliferation by inducing the apoptosis demonstrating that the biodegradable PLGAq microspheres will provide a promising therapeutic approach for the treatment of breast cancer.