Purpose: This study evaluated the five-year clinical performance of Dyract AP, a polyacid-modified resin composite, in restorations of Class I carious lesions. Materials and Methods: One hundred eight Class I carious lesions in 21 patients were restored with Dyract AP. The lesions, which were macroscopically diagnosed with a probe, involved fissures. The average buccolingual width of the cavities was equal to or less than one-third of the intercuspal width. Restorations were clinically evaluated by two experienced, calibrated examiners at baseline and at 1, 2, 3, 4, and 5 years, utilizing the modified Ryge criteria. The evaluation criteria included color match, marginal discoloration, wear or loss of anatomical form, caries, marginal adaptation, and surface texture. Results: At the end of the 5-year period, a total of 13 restorations had failed, and the cumulative rate of success was 93.37%. By the 5-year recall, 12 restorations had carious lesions adjacent to the margins, and 1 restoration had discoloration that was rated as Charlie. Color changes, marginal discoloration, wear or loss of anatomical form, caries, marginal adaptation, and change in surface texture were found to be statistically significant (p 0.001) after 5 years. Aside from the thirteen failed restorations, the degrees of color matching, marginal discoloration, wear or loss of anatomical form, caries, marginal adaptation, and surface texture were clinically acceptable at 5 years after treatment. Conclusion: At the end of 5 years, Dyract AP exhibited acceptable clinical performance in the treatment of Class I carious lesions. Therefore, it can be considered an alternative material for the restoration of Class I cavities. Keywords: Dyract AP, polyacid-modified resin composite, Class I carious lesions, clinical performance