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controlled release; chitosan; hydroxypropyl methylcellulose. The objective of present study was to develop controlled release lamivudine microspheres using spray drying encapsulation technique to increase the efficacy of anti retroviral drug, lamivudine against HIV infections and decrease its gastric unwanted effects. Low and high molecular weight chitosan and hydroxypropyl methylcellulose (HPMC) in different drug-polymer ratios were used for the preparation of microspheres. A 32 factorial experimental design was employed to explore the effect of polymer type (X1) and drug percentage (X2) on the release rate of the drug from the microspheres. The yield value (Y1), encapsulation efficiency (Y2), particle size (Y3) and the release efficiency percentage (Y4) were selected as the dependent variables. Drug release from microspheres was compared with the release behavior of commercially available formulation Lamidine®. The best encapsulation efficiencies were obtained when chitosan of low molecular weight (CL) or HPMC were used for microencapsulation. Tissue Culture Infective Dose that causes CPE for 50 % of cells (TCID50) was calculated using Reed-Muench formula. TCID50 of the prepared formulae was higher than TCID50 of Control after 5 hours. Marked retardation of lamivudine release from its prepared microspheres indicates the success of controlling drug release over 5 hours