Novel crystals of a pyrrolidylthiocarbapenem derivative having excellent stability is provided. According to the present invention, a crystal of (+)-(4R,5S,6S)-6-[(1R)-1-hydroxyethyl]-4-methyl-7-oxo-3[[(3S,5S)-5-(sulfamoylaminomethyl)pyrrolidin-3-yl]thio]-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid having a diffraction pattern in powder X-ray diffraction having main peaks at diffraction angles (2θ) of about 6.62, 13.04, 15.44, 16.58, 17.64, 20.88, 23.26, 25.02 and 25.52 (degrees) are provided.
