The invention provides a
baricitinib polymorph A. The
baricitinib polymorph A is characterized in that
diffraction peaks are arranged on an XRPD (
X Ray Powder Diffraction) map when values of 2 theta are equal to 12.46, 13.921, 14.94, 15.359, 16.26, 16.639, 17.36, 19.08, 20.321, 21.961, 22.381, 24.118, 25.42, 27.441, 28.381, 29.321, 29.799, 32.675, 33.14, 33.563, 33.923 and 41.6, wherein an error range of the values of the 2 theta is + / - 0.2. The
baricitinib polymorph A provided by the invention has good high-temperature stability, good high-
humidity stability and good illumination stability, can be applied to
medicine for treating or preventing diseases related to JAK (
Janus Kinase) and has better
biological availability; meanwhile, provided qualitative and quantitative information has important significance in further studying the
therapeutic effect of such
solid medicine.