Apatite ores type III of Lao Cai area, Vietnam is a class of weathered sileceous apatite ores, which may have most variable composition and primary slime content according to the weathering level and location. The three operating flotation plants use similar single-stage grinding circuits to process the highly weathered sileceous apatite ores and to achieve the concentrate grade requirement of 31% P2O5 with the aimed average recovery of about 70%. Single stage grinding circuits have worked well in the past as the designed criteria were achieved, however, mine production has increased sharply and deeper ores are being mined recently, so that the material composition of the run of mine ores have become more complicated and are the ores become more difficult to be floated. As a result, processing criteria of these plants become critically unstable and low. The study is to investigate the suitabity of two-stage grinding circuits for Lao Cai apatite ore type III. The report presents the results of the study on middlings regrinding of hard floatable apatite samples of Bac Nhac Son flotation plant, where high loss of valuable apatite has occured due to low grinding performance. Research results show that regrinding of all middlings to the fineness of 75% -0.04mm not only improves recovery but also help to stabilize technological operations and their processing criteria. The final concentrate grade of more than 31% P2O5, tailings content of less than 5% P2O5 and recovery of over 70% were achieved.