The majority of BIA parameters have been investigated in relation to post-stroke recovery, except for body cell mass (BCM), which measures the body’s cellular components involved in oxygen consumption and nutritional status. The aim of this longitudinal prospective study was to investigate in a cohort of subacute post-stroke patients undergoing rehabilitation the body composition parameters from BIA and the relationship between these parameters, in particular BCM, with both the performance in activity of daily living (ADL), measured by Barthel’s Index at admission (BI T0), and the recovery in ADL, measured by change in BI from baseline (ΔBI). We analyzed 66 patients, before and after a six-week rehabilitation program and we found that patients’ body composition after the rehabilitation protocol did not change. All lean mass and muscle quality parameters measured by BIA are positively correlated with BI T0. Moreover, patients with better recovery had higher values of BCM, such as other lean mass parameters and their related height-adjusted indices. Furthermore, BCM was independently associated both with ADL performance at admission, and most notably with recovery. These results suggest that assessing BCM at admission not only would improve the valuation of the nutritional status in post-stroke patients but would also potentially predict their recovery.