Biodegradable nanospheres based on a symmetric PLGA-PEG-PLGA triblock copolymer were prepared and investigated for insulin encapsulation and release. A PLGA-PEG-PLGA copolymer with a lactide (LA)-to-glycolide (GA) ratio of 3:1 was obtained by thering-opening polymerisation method and characterised via 1HNMR and gel permeation chromatography. The gelation temperatures of different concentrations of copolymer solutions were measured using the inverted test tube method. Nanospheres were prepared in an aqueous solution of 6.6% w/v of copolymer and 1.33% w/v of insulin without using any organic solvent. This new encapsulation method utilised the thermogelling property of the copolymer in the procedure. Under optimum conditions, uniform insulin nanospheres, 230 nm in size, were obtained. Insulin release from the nanospheres was investigated using spectrofluorimetryat le xcitation=280 nm and l emission=303 nm. The number average molecular weight of the copolymer was found to be 4743, and the sol-gel transition temperatures were in the 16–19°C range in terms of copolymer concentration. Drug loading within the nanospheres was about 20%. The insulin release profile exhibited an initial burst release (~30%) followed by a sustained release over three weeks (>85%). The obtained results suggest that nanospheres prepared with this new thermogelling method are a good candidate for encapsulation and insulin release.