The crystal of the invention is crystal of diphenylmethyl 2-methyl-2-triazolylmethylpenam-3-carboxylate which is stable substantially without decomposition or degradation of properties even when left to stand at room temperature for 1 year. The crystal of the invention can be prepared by a process comprising the steps of concentrating a solution containing diphenylmethyl 2-methyl-2-triazolylmethylpenam-3-carboxylate represented by the formula (2)
wherein Ph is a phenyl group, diluting the concentrate with acetic ester and mixing the diluted solution with hexane or a solvent mixture of hexane and acetic ester to crystallize the diphenylmethyl 2-methyl-2-triazolylmethylpenam-3-carboxylate.