Vascular cognitive impairment is frequent, in mild (mVCI) or severe forms (vascular dementia). To do a randomized controlled-trial to evaluate the impact of physical activity on cognition (primary outcome), neurocognitive measures, quality of life, functional status, and physical function (secondary outcomes), in patients with mVCI. A hundred and four patients with mVCI (mean age 71.2 years; 53 women) were randomized for a six-month intervention of moderate physical activity (60-minute sessions, 3 times/week) (n = 53) or best-practice "usual care" (n = 51). Comprehensive evaluations of primary and secondary outcomes included an objective measure of physical activity through accelerometry at baseline and after intervention. Mean session attendance was 58%. Adverse events were negligible. After 6 months, no significant primary outcome change was observed, either in the intervention or 'usual care' group. The intervention group improved significantly in some secondary outcomes in physical function - aerobic capacity (U = 403; p = 0.000) and agility (U = 453; p = 0.005) after 6 months. Regardless of randomization arm, a post-hoc analysis based on fulfilling at least 21.5 minutes/day of moderate or 10.7 minutes/day of vigorous physical activity (World Health Organization-WHO standards) revealed improvements. These were not only in motor capacity but also on the global measure of cognition, executive functions and memory. Physical activity was safe and beneficial regarding domains of physical function. No significant cognitive decline was registered over 6-months, regardless of intervention allocation. Larger samples, longer follow-ups and focus on intervention adherence are needed to fully analyze the impact of WHO recommendations for physical activity in mVCI populations.