With its ability to cross the blood-brain barrier, temozolomide (TMZ) is the first-line treatment option in glioblastoma multiforme therapy. This study aims to design TMZ-loaded PLGA nanoparticles (TMZ-PLGA-NP) in a thermoreversible hydrogel system comprising Pluronic® F-127. TMZ-PLGA-NP were prepared via emulsion-solvent evaporation method using dimethylformamide (DMF) as organic solvent and PVA solution as stabilizer. Experimental parameters for the formulation process and in vitro release profiles of free drug, TMZ-PLGA-NP and TMZ-PLGA-NP-loaded in hydrogel were investigated. Particle size in the range of 100–200 nm with an encapsulation efficiency of 55–70% has been obtained. In vitro studies showed that the TMZ-PLGA-NP loaded in hydrogel formulations have significantly slowed down the release process, providing controlled and sustained release. These nanoparticles were efficiently taken up by the glioblastoma cells and the TMZ released from the TMZ-PLGA-NP-loaded in hydrogel could reach to the efficiency of direct exposure to the free-drug. In conclusion, the thermoreversible hydrogel system containing TMZ-loaded PLGA nanoparticles may serve as a promising approach that could sustain long-term drug release for the treatment of residual glial tumors after surgery.