Abstract: Objective: To compare the performance of the modified caries-risk assessment tool for preschool children (PSC-MCAT) and the Cariostat caries activity test in predicting caries risk among young children in Xixiangtang District, Nanning, Guangxi, and to verify the feasibility of PSC-MCAT in predicting caries risk in young children in Guangxi. Methods: A prospective cohort study enrolled 511 three-year-old children from kindergartens in Xixiangtang District, Guangxi. At baseline, their caries risk was assessed with both PSC-MCAT and Cariostat. Comprehensive oral examinations were performed every six months for 1.5 years to compare the effectiveness of the two methods in predicting incident caries. Results: No statistically significant difference was observed in the caries risk levels assessed by the two methods (P＞0.05), and their agreement was poor (P＜0.05). At the 1.5-year follow-up, statistically significant differences in the mean new caries count were found among all three risk levels of the PSC-MCAT (P＜0.05). For the Cariostat, significant differences were only observed between the low-risk and high-risk groups and between the moderate-risk and high-risk groups (P＜0.05); within each baseline caries-risk level, no statistically significant differences in 1.5-year caries incidence or increment were observed between the two CRA methods for low- and moderate-risk children (P＞0.05). In the high-risk group, statistically significant differences were observed in both caries incidence and increment (P＜0.05). Generalized linear model analysis revealed a positive association between the risk levels assessed by both tools and the incidence of new caries. In the low- and moderate-risk levels, PSC-MCAT did not differ significantly from Cariostat (P＞ 0.05). In the high-risk level, a statistically significant difference was observed between the PSC-MCAT and Cariostat (P＜0.05), and PSC-MCAT was associated with an increased risk of new caries development (P＜0.05). The area under the receiver operating characteristic (ROC) the curve (AUC) for the PSC-MCAT was 0.634 (95% CI: 0.593-0.675), with a sensitivity of 92.55% and a specificity of 32.62%. The Cariostat yielded an AUC of 0.664 (95% CI: 0.622-0.701), with a sensitivity of 24.45%, and a specificity of 94.76%. Conclusion: The PSCMCAT demonstrates considerable potential for caries risk assessment and prediction of new caries development, showing particular advantage in the initial screening of high-risk individuals.