This article examines the effects of Montessori music-movement activities on the development of the rhythmic abilities of 59 children from Montessori preschools, aged between 3 and 6 years. Children were deployed into two experimental groups (EG 1 (n = 20) & EG 2 (n = 22)) and a control group (CG) (n = 17). Our intervention consisted of introducing 15 to 20 min of unstructured movement time, either accompanied by a piano (EG 1) or recording (EG 2), three times a week for four months, whereas the control group carried on the usual Montessori program. We used a quasi-experimental nonequivalent groups design with pretest-posttest. Three tests for measuring rhythmic abilities were used: auditory discrimination of the rhythmic patterns, imitation of spoken rhythmic phrases, and determining the synchronization of movement with the rhythm of the music. The interventions had a positive effect on the development of the rhythmic abilities of children included in the study. The most significant effect was noticed in EG 1, while no effect of non-activity was detected in the control group.