Abstract: To study the rheological properties of sucrose acetate isobutyrate (SAIB) in situgel and the influencing factors. Measurements of shear stress and viscosity were carried out at different shear rate. The rheological properties of SAIB solution were similar to those of Newtonian fluid. The factors such as the type of solvent, concentration, additive, drug and temperature had effect on the rheological properties. Ethanol was a suitable solvent compared with ethyl lactate and N-methylpyrrolidone (NMP). The solution viscosity of SAIB was reduced from 1.29 to 0.11 Pa·s with only increasing the content of ethanol from 10% to 20%. Polylactic acid (PLA) and risperidone could increase the intermolecular force and viscosity. However, adding 10% (w/w) PLA, the initial release of risperidone was reduced from 20.2% to 3.5%. The solution viscosity reduced significantly by stepping up the temperature. The results obtained support the using of SAIB is satisfactorily injectable in situgel formulation.