Purpose: To investigate if physical activity (PA) support could increase PA and health-related quality of life (HRQoL) in patients isolated after haematological stem cell transplantation, compared with standard care. Methods: A prospective historical control group design was used. Patients were sequentially included in a standard care group (SCG, n=22) or a physical activity support group (PASG, n=21). PASG patients received PA support at a pre-transplantation consultation, daily during admission, and at follow-up 14 days post-discharge. All participants undertook a 6-minute walking test (6MWT) at the beginning and end of their hospital stay. HRQoL was evaluated using the Functional Assessment of Cancer Therapy – Anaemia scale. Patients reported all PA, including sitting, throughout their hospital stay. Metabolic Equivalents of Task (METs) were calculated. Results: PASG patients spent more time sitting and doing various activities, and less in bed, than SCG patients (p=0.03–0.06). They had more calculated METs for total PA out of bed (p=0.02) and time spent sitting (p=0.05). PASG patients walked further in the 6MWT than SCG patients at baseline (p=0.02) and at discharge, but not significantly. There were no statistically significant differences in HRQoL, but PASG patients had clinically important less fatigue at discharge and clinically important better HRQoL 6 months post-discharge. Conclusions: Providing stem cell patients, pre-transplantation, with individual care plans for structured PA support during the hospital stay might increase PA and have a clinically important impact on HRQoL. Larger studies are needed to evaluate the effects of PA support on medical outcome and length of hospital stay.