Introduction: Previous studies indicated that the amount of time spent playing online games is a significant predictor of decline in cognitive function. Cognitive Functioning Self-Assessment Scale (CFSS) is used to measure the self-assessment of perceived cognitive functioning. This study aimed to analyze the validity and reliability of the Indonesian version of CFSS (CFSS-Ina) in online game users. Method : A cross-sectional study of 194 participants was conducted online. Content validity was assessed with Aiken’s V. Construct validity consists of convergent validity, measured using average variance extracted (AVE), and discriminant validity, measured by calculating heterotrait-monotrait ratio (HTMT) correlation. Factor analysis was performed using principal component analysis (PCA). Internal reliability was assessed using Cronbach’s alpha and test-retest reliability with intraclass correlation coefficient (ICC). Results: Aiken’s V value exhibited a high content validity (0.90). For convergent validity, AVE value was 0.429, whilst CR value was 0.93. Discriminant validity was statistically significant (HTMT = 0.562). Outer loading of CFSS-Ina ranged from 0.509 to 0.778. Cronbach’s alpha coefficient for construct reliability was 0.92, whilst ICC for test-retest reliability was 0.899. Conclusion: CFSS-Ina is a valid and reliable self-assessment tool to detect early signs of perceived cognitive impairment in online game users.