Polypyrrole nanospheres synthesized by using the ultrasonic method were sulfonated with concentrated H2SO4 at different tempeartues. The catalytic performance of the sulfonated polypyrrole nanospheres in the esterification of methanol with acetic acid was evaluated and compared with that of sulfonated carbonized polypyrrole nanospheres. The surface chemistry and structure of the samples were investigated using X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectrometry, thermogravimetric analysis, nitrogen adsorption and elemental analysis techniques. The morphology of samples was characterized with field-emission scanning electron microscopy and transmission electron microscopy. The results showed that low carbonization and sulfonation temperatures are favorable for enhancing the catalytic activity and recyclability of the solid acid catalysts.