Abstract: Tilmicosin starch microsphere were synthesized with soluble starch as material and N，N′-methylene-bis-acrylamide as crosslinking agent by using pack cementation method. The preparation process was optimized through the L9(34) orthogonal experimental design and regression analysis based on the evaluation indicators of the drug loading and encapsulation efficiency. Tilmicosin starch microsphere inclusion compound was characterized by laser particle analyzer，scan electron microscope and thermogravimetric analysis (TGA). The results indicated the best technological conditions was that: the quantity of soluble starch，tilmicosin，N，N′-methylene-bis-acrylamide and surfactant was
4，0.02，0.95，0.75 g respectively and the reacting time was 1 h. Influence factors were the quantity of N，N′-methylene-bis-acrylamide，the quantity ratio of tilmicosin to soluble starch，the reacting time，the quantity of emulsifier in order. The drug loading and embedding ratio were respective 2.24% and 89.6% by optimizing conditions. The retarded release could be observed and this preparation method was reasonable and feasible.

Key words: starch microsphere; tilmicosin; pack cementation method; regression analysis; drug release in vitro