mesenchymal stem cells (mscs) can be affected in their capabilities to proliferate in vitro under physical and/or biochemical stimulation. the aim of this study was to select an optimal intensity level for low intensity pulsed ultrasound (lipus) stimulation of sprague-dawley bone marrow mscs proliferation in vitro. bone marrow mscs of sprague-dawley rats where cultured (a-mem, 20%fbs and 1%antibiotic) and stimulated with lipus (0,02 milisec), for 20 minutes twice daily for 10 days, at intensities of 0 (control), 30 and 50mw/cm2 (groups a, b, c). cellular count and morphological evaluation were performed. anova and bonferroni tests were performed. lipus-stimulated cultures displayed greater cellular counts, and significant differences were observed between groups a and c (p<0,05). morphological differences were observed between cells from lipus-stimulated and control groups. an intensity of 50mw/cm2 elicits increased cellular proliferation (p<0.05). stimulation of mscs cultures with lipus influences cellular morphology.