The present work is the first study that assess long run change after motor learning. The study's main objective was to evaluate the short to medium-term impact of motor imagery (MI) and action observation (AO) on motor learning of a sequence of thumb-opposition tasks of increasing complexity. We randomly assigned 45 participants to an AO, MI, or placebo observation (PO) group. A sequence of 12 thumb-opposition tasks was taught for 3 consecutive days (4 per day). The primary outcome was accuracy. The secondary outcomes were required time and perfect positioning. The outcomes were assessed immediately after the intervention and at 1 week, 1 month and 4 months postintervention. Regarding the primary outcome, AO group had significantly higher accuracy than the MI or PO group until at least 4 months (p < 0.01, d > 0.80). However, in the bimanual positions, AO was not superior to MI at 1 week postintervention. Regarding secondary outcomes, AO group required less time than the MI group to remember and perform the left-hand and both-hand gestures, with a large effect size (p < 0.01, d > 0.80). In terms of percentage of perfect positions, AO group achieved significantly better results than the MI group until at least 4 months after the intervention in the unimanual gestures (p < 0.01, d > 0.80) and up to 1 month postintervention in the bimanual gestures (p = 0.012, d = 1.29). AO training resulted in greater and longer term motor learning than MI and placebo intervention. If the goal is to learn some motor skills for whatever reason (e.g., following surgery or immobilization.), AO training should be considered clinically.