Objective This study aimed to assess the reliability and validity of Japanese versions of the KIDSCREEN-27 (J-KIDSCREEN-27) and KIDSCREEN-10 (J-KIDSCREEN-10) questionnaires, which are shorter versions of the KIDSCREEN-52 (J-KIDSCREEN-52). Methods The present analyses are based on a pre-existing dataset of the J-KIDSCREEN-52 validation study, including 1564 children and adolescents aged 8-18 years and their 1326 parents. All were asked to complete the J-KIDSCREEN and Pediatric Quality of Life Inventory (PedsQL) questionnaires. Test-retest reliability was assessed with Intraclass Correlation Coefficients (ICCs) in a one-way random effects model, and internal consistency reliability was measured using Cronbach's alpha coefficients. Agreement between child and parent scores was evaluated using ICCs in a two-way mixed effects model. To assess concurrent validity, a sub-sample of 535 parents evaluated their child's mental health status using the Strengths and Difficulties Questionnaire (SDQ).Results For children, test-retest ICCs were C0.60 and Cronbach's alpha C0.70 for every dimension of both instruments. Correlations of corresponding dimensions between the J-KIDSCREEN-27 or -10 and the PedsQL were acceptable. For parents, test-retest ICCs were C0.60, Cronbach's alpha C0.70, and ICCs between child and parent scores C0.41 in every dimension of both instruments. In multivariate logistic regression models, after adjusting for confounders, lower health-related QOL in every dimension of both instruments, except Physical Well-being, was significantly associated with higher odds ratios for borderline and clinical ranges of the SDQ. Conclusion The child/adolescent and parent/proxy versions of the J-KIDSCREEN-27 and J-KIDSCREEN-10 demonstrated acceptable levels of reliability and validity.