The sleep quality of patients with osteosarcoma (OS) was poorly understood. We aimed to evaluate the prevalence of sleep dysfunction in adolescent patients with OS using the Pittsburgh Sleep Quality Index (PSQI) and to further investigate the psychometric properties of the PSQI in this cohort of patients. Fifty four adolescent patients with OS who underwent chemotherapy treatment in our clinic centre were included. Sleep quality was assessed with the Chinese PSQI. Cronbach's alpha was calculated to evaluate the internal consistency. The confirmatory factor analysis (CFA) was used to determine the fitness of a two‐factor structure. Sleep disturbance was observed in 57.4% (31/54) of the patients. Patients with the presence of metastasis or more than 2 cycles of chemotherapy were found to have remarkably higher median global score. The overall Cronbach's alpha was 0.87. The CFA showed an overall comparative fit index of 0.97, a root mean square error of approximation of 0.06 and a standardised root mean square residual of 0.07 respectively. PSQI was a reliable instrument to evaluate the sleep quality of adolescent patients with OS. Over half of the patients may experience sleep disturbance during the treatment. Early psychological interventions were recommended to improve the sleep quality of the patients.