Phosphonocephem compound

A cephem compound (particularly its crystal) represented by the formula [I], wherein X is CH₃COOH, CH₃CH₂COOH or CH₃CN, and n is 0 to 5, is useful as an antibacterial agent (particularly anti-MRSA agent) and shows superior quality such as high solid stability, possible long-term stable preservation and the like. ##STR1##