PROBLEM TO BE SOLVED: To provide novel polymorphic forms of moxifloxacin hydrochloride with high product yield and quality, and a simple, safe and cost effective process for producing the polymorphic forms.SOLUTION: Moxifloxacin hydrochloride Form C characterized by having an XRPD with peaks at 15.08, 27.86 and 28.22°2&thetas;±0.2°2&thetas; is obtained by: condensing the borate complex of the formula (I) with (S,S)-2,8-diazabicyclo[4.3.0]nonane in an organic solvent to obtain an intermediate (II); hydrolyzing the intermediate (II); and then treating it with methanolic hydrochloric acid.【課題】高い生成物収率及び品質のモキシフロキサシン塩酸塩の新規な多形、及び該多形をつくるための単純で安全でコスト効率の良い方法の提供。【解決手段】ボレート複合体、式(I)を(S,S)-2,8-ジアザビシクロ[4.3.0]ノナンと有機溶媒中で縮合させて中間体(II)、該中間体(II)を加水分解、次いでメタノール性塩酸処理して15.08、27.86および28.22°2θ±0.2°2θにピークをもつXRPDを有することにより特徴づけられるモキシフロキサシン塩酸塩C型を得た。【選択図】図1