Poly(p-phenylene sulfonic acid) microspheres were prepared by a simple, green and controllable method, and used as solid acid catalysts for the synthesis of biodiesel. Firstly, poly (p-phenylene sulfonic acid) microspheres (PSS) were prepared by soap-free emulsion polymerization with water as medium, styrene (St) as the matrix monomer, divinylbenzene (DVB) as the cross-linking monomer, sodium p-phenylene sulfonate (NaSS) as functional monomer, methacrylic acid (MAA) as the water-soluble monomer, and potassium persulfate (KPS) as the initiator. The obtained microspheres were characterized by FT-IR, XPS, SEM, TGA and DSC, and their particle size, zeta potential, specific surface area and acid density were investigated. The effects of NaSS, DVB and KPS contents on the structure and properties of the microspheres were discussed. Then, PSS was used as solid acid catalyst to catalyze the esterification of oleic acid/methanol to synthesize biodiesel. The conversion rate of oleic acid could reach 86.4% when the ratio of methanol to oleic acid is 10:1, the amount of PSS is 2% of the mass of oleic acid, the reaction temperature is 80 ℃, and the reaction time is 6 h. As a solid acid catalyst, PSS has good reusability, and the conversion of oleic acid has not decreased significantly after 4 cycles.