The crystal of the invention is the crystal of diphenylmethyl 2-methyl-2-triazolylmethylpenam-3-carboxylate 1,1-dioxide which is stable substantially without decomposition or degradation of properties even when left to stand at a temperature of 5 to 35 DEG C for a period of 1 year. The crystal of the invention can be prepared by adding diphenylmethyl 2-methyl-2-triazolylmethylpenam-3-carboxylate 1,1-dioxide represented by the formula (1) wherein Ph is a phenyl group, in the form of oily substance or in the form of amorphous powder or an organic solvent solution thereof to at least one species selected from alcohols and ketones to crystallize the diphenylmethyl 2-methyl-2-triazolylmethylpenam-3-carboxylate 1,1-dioxide. |