Objective: To prepare and in vitro evaluate the self-microemulsifying drug delivery system (SMEDDS) of adefovir dipivoxil (ADV).Methods: The optimized formula was screened by solubility, compatibility, ternary phase diagram and orthogonal design with the self-emulsifying time and particle size of microemulsion as the indices.The property of self-emulsification and the dissolution in vitro of ADV-SMEDDS were also determined.Results: The optimized SMEDDS was composed of Cremophor EL35 (37.5%), Transcutol HP (37.5%) and PECEOL (25%), and the drug loading was 3%.The ADV-SMEDDS formed stable microemulsion after the dilution by 50-fold amount of water in 24 s, the average particle size was (26.30±0.46) nm, the zeta potential was (-8.96±0.57) mV, and the dissolution was more than 85% in 5 min.Conclusion: The optimized formula of ADV-SMEDDS has significantly enhanced solubility and dissolution of adefovir dipivoxil in vitro.