Objectives: study was carried out on 34 fully edentulous patients in Hanoi University of Medicine. The aim of this study was to compare the accuracy of two impression taking methods. Method: For the same patient, the authors took two impression methods with alginate: the conventional primarily impression and the relining primarily impression. Then, the models were made. The retention force value was measured. Results: For the conventional primarily impression, the retention force values were: minimum: 0.175kg, maximum: 0.567 kg, medium: 0.321kg. For the relining primarily impression, the retention force values were: minimum: 0,2 kg, maximum: 0.623 kg, medium: 0.425kg. Conclusions: The relining primary impression showed a more accurate model in comparison to the conventional primary impression.