BACKGROUND Blood cancers account for 7% of all malignant neoplastic diseases worldwide. However, there has been an increase in the survival rate of patients with hematological cancer. These data indicate the need to make patients aware of the importance of physical activity. We aimed to assess the level of physical activity and sedentary lifestyle of patients with hematological cancer treated with monoclonal antibodies as a monotherapy or combination therapy (immunochemotherapy), compared with that of healthy individuals. MATERIAL AND METHODS Patients (n=155) treated for hematological malignancies (study group) and healthy individuals (n=137) were divided using World Health Organization (WHO) recommendations on physical activity into groups of adults aged 18-64 years and 65 years and older. All participants completed the International Physical Activity Questionnaire (IPAQ). RESULTS In the younger adult group, the median IPAQ total score in the study group was 1235.00 compared with 3186.00 in healthy individuals (P<0.0001). Importantly, the study group also differed from healthy individuals in terms of sitting time: 1200.00 vs 360.00 (P<0.0001). In the older adult group, no significant difference was found in the median IPAQ total score: 1188.00 vs 1777.00 (P=0.25); however, significant differences were observed for sitting time: 900.00 vs 300.00 (P<0.0001). CONCLUSIONS Patients with hematological cancer treated with monoclonal antibodies as a monotherapy or combination therapy (immunochemotherapy) show, regardless of age, lower levels of physical activity and longer sitting time than healthy individuals, indicating the need for education and promotion of physical activity in this group of patients.