This work aimed to evaluate polyhydroxyalkanoates (PHA)-accumulating aerobic granular sludge (AGS) production using an inoculum of activated sludge and a prefermented medium consisting of leachates from the anaerobic hydrolysis of the organic fraction of municipal solid waste (OFMSW). Operating conditions induced the evolution in the biomass structure to obtain aerobic granules with an average diameter of 1 mm within the first 45 days. This process resulted in remarkable evolution in the settling properties, with a four-fold improvement in the sludge volume index (SVI) and the zone settling velocity (Vs), as well as a considerable increase in the density during the same period. Moreover, AGS exhibited a maximum PHA accumulation capacity of 0.215 g-PHA/g-VSS, which was two-fold higher than in the inoculum, indicating the enrichment of the biomass on PHA-accumulating microorganisms as a result of the application of the anaerobic feeding of the substrate and the operation with long famine periods; operating conditions reported as favorable for both, the cultivation of stable AGS and the selection biopolymers-accumulating microorganisms. However, the carbon balance revealed that VFA from the leachates was preferably used for EPS synthesis instead of PHA production, showing that microorganisms in AGS absorb organic carbon to convert it into EPS for internal structure maintenance.