ObjectiveThis cross-sectional study aimed to investigate socioeconomic inequalities in dental caries among adults (35 years and older) in China and explore the contributions of various factors to these inequalities.MethodsThis study included 10,983 adults (3,674 aged 35–44 years, 3,769 aged 55–64 years and 3,540 aged 65–74 years) who participated in the 4th National Oral Health Survey (2015–2016) in China. Dental caries status was evaluated by the decayed, missing and filled teeth (DMFT) index. Concentration indices (CIs) were applied to quantify the different degrees of socioeconomic-related inequality in DMFT, decayed teeth with crown or root caries (DT), missing teeth due to caries or other reasons (MT), and filled teeth without any primary or secondary caries (FT) among adults of different age groups. Decomposition analyses were conducted to identify the determinants and their associations with inequalities in DMFT.ResultsThe significant negative CI indicated that DMFT for the total sample were concentrated among socioeconomically disadvantaged adults (CI = − 0.06; 95% confidence interval [CI], − 0.073 to − 0.047). The CIs for DMFT for adults aged 55–64 and 65–74 years were − 0.038 (95% CI, − 0.057 to − 0.018) and − 0.039 (95% CI, − 0.056 to − 0.023), respectively, while the CI for DMFT for adults aged 35–44 years was not statistically significant (CI = − 0.002; 95% CI, − 0.022 to 0.018). The concentration indices of DT were negative and concentrated in disadvantaged populations, while FT showed pro-rich inequalities in all age groups. Decomposition analyses showed that age, education level, toothbrushing frequency, income and type of insurance contributed substantially to socioeconomic inequalities, accounting for 47.9%, 29.9%, 24.5%,19.1%, and 15.3%, respectively.ConclusionDental caries was disproportionately concentrated among socioeconomically disadvantaged adults in China. The results of these decomposition analyses are informative for policy-makers attempting to develop targeted health policy recommendations to reduce dental caries inequalities in China.