The research was carried out on 26 children at the high dentistry technology centre of School of Odonto Stomatology and Ha Noi Medical University hospital. The goal was to evaluate the effect of preformed stainless steel crowns in primary molars. Reasearch methodology: clinical trial without controlled group. Clinical examination and radiographs were performed 6 months after restoration of primary molars with preformed stainless steel crowns. To evaluate the conditions of gingivitis, sealing, loose crowns, contact area and occlusal at this time. Results: 4 percent gingivitis
5,33 percent loose crowns
86,67 percent sealing well
93,33 percent suitable occlusal
94,67 percent good contact area. Conclusion: The effect of preformed stainless steel crowns in primary molars is very good.