An object of the present invention is to provide a solid composition comprising a stabilized salt of aminocarboxylic acid. The object can be attained by a pharmaceutical solid composition comprising [(1R,5S,6S)-6-(aminomethyl)-3-ethylbicyclo[3.2.0]hept-3-en-6-yl]acetic acid monobenzenesulfonate which is compound represented by the following formula (I) in combination with appropriate additives.