Increasing physical activity level during and after treatment is recommended by the American Cancer Society because of the many benefits namely reducing fatigue and improves psychological distress which leads to an improvement in the quality of life. This study is aimed to compare physical activity level and body composition between oncology patients who are still undergoing treatment and those on medical follow-up. Patients were recruited based on convenience sampling from the Oncology Outpatient Clinics of Universiti Kebangsaan Malaysia Medical Center (UKMMC). Anthropometric measurements and body compositions were measured using calibrated tools while physical activity level were assessed using Global Physical Activity Questionnaire (GPAQ). Medical treatment history was obtained from patients medical records. A total of 53 patients (n=38 were undergoing treatment and n=15 was on follow-up) consisting of Malays (54.7%) and Chinese (45.3%) and with mean age of 55.3 ± 9.3 years. Most patients were previously diagnosed with ovarian cancer (39.6%) and colon cancer (18.9%) patients and they were at cancer stage III (18.8%). Body mass index (BMI) and percent fat mass were significantly different (p<0.05) between patients undergoing treatment (22.8 ± 2.7 kg/m2, 28.7 ± 7.2%) and on follow-up (26.2 ± 5.5 kg/m2, 37.1 ± 11.9%). Majority of the patients undergoing treatment were categorized under low physical activity compared to those on follow-up (p<0.05). Physical activity level measured as METS-minutes/week is also found to be significantly different (p<0.05) between patients on treatment and follow-up. As a conclusion, cancer patients undergoing treatment have low physical activity, with lower BMI and fat mass compared to those on follow-up. This is consistent with their nature of living where during treatment the patients will resting while coping with side effects of treatments.