Background Patients with rheumatic disease are assumed to have low muscle performance, but few studies have been performed to prove this. Objective To investigate and compare muscle performance in rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) patients and detect its correlation with disease activity, physical function level and quality of life. Patients and Methods Fifty RA patients, 50 SLE patients and 50 healthy controls were recruited for this observational, cross-sectional study. Muscle performance tests for the upper and lower limbs and the fatigue severity score were recorded. Assessments of the physical activity level using the frequency intensity time index and quality of life using the SF36 questionnaire were performed. The study was conducted over 4 months from January to April 2019. Results SLE patients showed better results of muscle performance than RA patients; however, both had lower results as compared to control. Disease activity was correlated to muscle performance tests in both diseases, except for the 30-second chair stand test in SLE (p=0.247). All domains of SF36 had a significant correlation with the performance tests in SLE (p≤0.05); however, only domains of physical function correlated with the tests in the RA group. Conclusion RA patients tend to have a lower muscle performance and physical activity level as compared to SLE patients and control.