Abstract： Aim To compare the efficacy of Nd:YAG laser and Er:YAG laser assisted treatment for severe periodontitis,and analyze their effects on the levels of matrix metalloproteinase(MMP),prostaglandin E2(PGE2),and inflammatory factors in gin-gival crevicular fluid.Methods 108 patients with severe periodontitis were selected and randomly divided into Nd:YAG group and Er:YAG group.The clinical efficacy,periodontal health indicators,and gingival crevicular fluid related indicators between two groups were compared.Results There was no significant difference in the total effective rate between the two groups(P＞0.05).Compared with before treatment,PLI,PD,BI,and CAL were decreased in both groups after treatment,and the decrease in CAL in the Er:YAG group was more significant than that in the Nd:YAG group,the decrease in BI in the Nd:YAG group was more signifi-cant than that in the Er:YAG group(P＜0.05).Compared with before treatment,MMP-8,MMP-9,PGE2,inflammatory factors levels in both groups after treatment were decreased(P＜0.05),but there was no difference between the two groups(P＞0.05).Conclusion Both Nd:YAG laser and Er:YAG laser have good adjuvant treatment effects on severe periodontitis,but Er:YAG laser improves periodontal tissue attachment more significantly,and Nd:YAG laser has better hemostatic effect.