Objective To investigate the effect of lithium disilicate ceramic onlay on masticatory efficiency and aesthetic satisfaction in patients with posterior tooth defect. Methods A total of 84 patients with posterior tooth defect admitted to Yangzhou Stomatological Hospital from January 2023 to January 2025 were selected as the research subjects. According to the random number table method, they were divided into the all-ceramic crown group and the onlay group, with 42 patients in each group. The all-ceramic crown group received lithium disilicate all-ceramic crown restoration, and the onlay group received lithium disilicate ceramic onlay restoration. The masticatory efffciency, aesthetic satisfaction and complication rate were compared between the two groups. Results At 12 months after restoration, the masticatory efffciency in the onlay group was higher than that in the all-ceramic crown group (P<0.05). The aesthetic satisfaction in the onlay group (100.00%) was higher than that in the all-ceramic crown group (88.10%) (P<0.05). The incidence of complications in the onlay group (2.38%) was lower than that in the all-ceramic crown group (19.05%) (P<0.05). Conclusion Lithium disilicate ceramic onlay can not only improve masticatory function of posterior teeth and reduce the incidence of complications, but also enhance patients’ satisfaction with aesthetic effect.