BACKGROUND AND OBJECTIVES: Simultaneous bilateral total knee arthroplasty (SBTKA) can improve post-surgical outcomes and reduce complications and cost of care. This study aimed to compare: (a) pain intensity levels in patients undergoing SBTKA between and before discharge, and 6 weeks after surgery, and (b) activities of daily living (ADL) and quality of life between the pre-operative period and 6 weeks after surgery. MATERIAL AND METHODS: Forty patients who were scheduled for SBTKA at inpatient units in a university-affiliated hospital in Bangkok, Thailand were recruited on the first day of admission using the face-to-face method. The research instruments included a demographic questionnaire, the Numeric Rating Scale (NRS), and the Knee and Osteoarthritis Outcome Score (KOOS): ADL, and knee-related quality of life subscales. The data were analyzed using descriptive statistics, paired t-test, and Wilcoxon Signed Rank Test. RESULTS: The results showed that the pain intensity level at six weeks after surgery was statistically significantly reduced when comparing the pre-discharge from the hospital (p = 0.000). Patients had improvements in their ADL (p = 0.000) and their quality of life (p = 0.000) at six weeks after surgery compared to before surgery. CONCLUSIONS: Patients who underwent SBTKA had clinical improvement in terms of pain intensity reduction and enhancement of their ADL and quality of life.