Abstract： Objective This study is to evaluate the sound effect of the co-prosthesis of a full crown and a half crown for patients who have two adjoining decayed molars. Methods 40 patients who had a largely decayed molar and a adjoining molar with contact point caries were included in the study. Co-prosthesis of a full crown and a half crown was used. All cases had been clinically observed for 3 to 5 years. Results One case was rebounded for the crown mobility. One abutment with pulpitis was re-treated with root canal therapy. Other cases were satisfied and the success rate was 95%. Conclusion This design can efficiently prevent food impaction and reduce tooth preparation.