Objective:To prepare DNA vaccine loaded sodium al ginate microspheres (DNA SA MS) and to evaluate its dissolution characteristic s in vitro . Methods: DNA SA MS was prepared with sodium al ginate as carriers by the water in oil ( W/O ) emulsion ion cross linking me thod . Physical and chemical characteristics of microspheres, such as mean diameter, morphology and drug loading were detected. The release characteristics in vitr o and its influencing factors were also detected. Results: Microspheres with good shape and dispersity were prepared. The mean diameters, d rug loading and drug entrapment efficiency were (12.03±6.9) μm, 5% and 56.0% r espectively. Release rate was negatively correlated with cross linking extent o f chitosan, positively correlated with the drug contents. Conclusion: Sodium alginate can be used as biodegradable carriers for the preparation of DNA vaccines microspheres and the microspheres can be used as ideal drug deli very system for DNA vaccines. The W/O emulsion ion cross linking method is simple and particularly good for the structural and functional integrity of DNA vaccines.