Methylene bisalkylphenols were synthesized by condensation reaction from alkylphenol and formaldehyde in an oxalic acid-catalyzed autoclave process, and the target products were identified by IR, ESI-MS and 1H-NMR. The experimental results showed that compared with normal pressure process autoclave process made the conversion of nonylphenol increased about 20 % and the selectivity of methylene bisnonylphenol elevated approximately 10 %. The effect of catalyst dosage, reaction time, temperature and substrate molar ratio on the condensation reaction were investigated one by one, and thus the conversion of nonylphenol was further improved and the selectivity of methylene bisnonylphenol was as high as 92.1 %. The condensation conditions for preparing methylene bisdodeylphenol in an autoclave process also were optimized by an orthogonal experiment. The experimental results showed that the autoclave process is a facile, low-cost and efficient technology to synthesize methylene bisalkylphenols, the precursor hydrophobic skeletons of Gemini surfactants.