In this work, we sought to generate sustained-release injectable microspheres loaded with the GLP-1 analogue liraglutide. Using water-in-oil-in-water double emulsion methods, poly(lactic-co-glycolic acid) (PLGA) microspheres loaded with liraglutide were prepared. The microspheres gave sustained drug release over 30 days, with cumulative release of up to 90% reached in vitro. The microspheres were further studied in a rat model of diabetes, and their performance compared with a group given daily liraglutide injections. Reduced blood sugar levels were seen in the microsphere treatment groups, with the results being similar to those obtained with conventional injections between 10 and 25 days after the commencement of treatment. After 5 and 30 days of treatment, the microspheres seem a little slower to act than the injections. The pathology of the rats' spleen, heart, kidney and lungs was probed after the 30-day treatment period, and the results indicated that the microspheres were safe and had beneficial effects on the liver, reducing the occurrence of fatty deposits seen in untreated diabetic rats. Moreover, in terms of liver, renal and cardiac functions, and blood lipid and antioxidant levels, the microspheres were as effective as the injections. The expression of several proteases linked to the metabolism of aliphatic acids and homocysteine was promoted by the microsphere formulations. Inflammatory markers in the microsphere treatment groups were somewhat higher than the injection group, however. The liraglutide/PLGA microspheres prepared in this work are overall shown to be efficacious in a rat model of diabetes, and we thus believe they have strong potential for clinical use.