Abstract: The viscosities of polylactic acid and poly (lactic acid-co-glycolic acid) solutions were determined by a rotary viscometer at different temperatures and concentrations, and the flow activation energies of polylactic acid and poly (lactic acid-co-glycolic acid) solutions were analyzed and calculated. The results show that the poly (lactic acid-co-glycolic acid) solutions exhibit the characteristics of pseudoplastic fluid and the viscosities of poly (lactic acid-co-glycolic acid) solutions decrease with the increase of theshear rate. The viscosities of poly (lactic acid-co-glycolic acid) and polylactic acid solutions increase with the increase of the concentration and decrease with the increase of the temperature. The exponential function can accurately reflect the relationship between viscosity and concentration of polylactic acid and poly (lactic acid-co-glycolic acid) solutions. The relationship between viscosity and temperature obeys the Arrhenius index function equation for polylactic acid and poly (lactic acid-co-glycolic acid) solutions.The flow activation energies of polylactic acid and poly (lactic acid-co-glycolic acid) solutions basically increase with the increase of concentration. The higher the flow activation energy of the solution, the more difficult the flow. And viscosity is the more sensitive to temperature variation. When the solvent and the concentration are certain, the flow activation energy of poly (lactic acid-co-glycolic acid) solution is lower than that ofpolylactic acid solution. The viscosity of poly (lactic acid-co-glycolic acid) solution is lower than that of polylactic acid solution. This demonstrates that the compatibility of poly (lactic acid-co-glycolic acid) and the solvent is better than that of polylactic acid, and this study also suggests that the liquidity of poly (lactic acid-co-glycolic acid) solution is better than that of polylactic acidsolution. Compatibility of polymer and solvent depends on the molecular structure of the polymer.