Abstract: Objective To study the clinical outcome of 90° steel plates in treatment of developmental hip dysplasia after proximal femur osteotomy. Methods Sixty-two children with developmental hip dysplasia involving 85 hips who underwent internal fixation with 90° steel plates after proximal femur osteotomy for proximal femur deformity. Results Fifty-five hips in 40 children with complete follow-up data were retrospectively analyzed.The patients were followed up for 7-96 months（mean 39.9 months） after operation.Bony union was achieved in these 55 hips 6 weeks after operation with satisfactory outcomes achieved in 52.The anteverted femur angle was 25°（range 15°-40°） and the neck-shaft angle was 30°（range 20°-40°）. Conclusion Fixation of proximal femur deformity with 90° steel plates is an effective procedure for children with developmental hip dysplasia.