A process for producing crystals of 4-[(5,6,7,8-tetra- hydro-5,5,8,8-tetramethyl-2-naphthalenyl)carbamoyl]benzoic acid exhibiting a single endothermic peak near 233°C in differential scanning calorimetry, which comprises the step of recrystallizing crystals of 4-[(5,6,7,8-tetrahydro-5,5,8,8 -tetramethyl-2-naphthalenyl)carbamoyl]benzoic acid from a water-ethanol mixture. This process enables selective production of type II crystals stable to physical impact, and the obtained crystals are free from highly toxic hexane as the residual solvent, thus being suitably usable as an active ingredient in medicines.