Objective The aim of this study was to analyze the effects of low-intensity pulsed ultrasound therapy under different pulse regimes on cultures of semiconfluent L929 fibroblasts, evaluating cell viability, anatomical structural alterations, modulation of vascular endothelial growth factor, interleukin 6, collagen type 1 alpha 1, collagen type 1 alpha 2, and fibroblast growth factor 7, as well as the amount of inflammatory mediators interleukin 2, interleukin 4, interleukin 6, interferon γ, tumor necrosis factor, interleukin 17A, and interleukin 10 at 24, 48, and 72 hrs. Design The design was experimental study. Methods The treatments consisted of 0.2 W/cm2 doses at a frequency of 1 MHz, with a pulse rate of 10% and 20%. Viability was assessed by the MTT assay (3-(4,5-dimethylthiazole)-2,5-diphenyltetrazolium bromide), gene expression by real-time quantitative polymerase chain reaction, and cytokine quantification by flow cytometry. Results At 48 hrs, ultrasound enhanced cell viability and affected interleukin 6 cytokine production, vascular endothelial growth factor, interleukin 6, type 1 alpha 1 and alpha 2 collagens, and fibroblast growth factor 7 gene modulation. Conclusions Low-intensity pulsed ultrasound therapy had a biostimulatory effect on semiconfluent in vitro L929 fibroblast cells, where the group with a dose of 0.2 W/cm2-10% (G2) presented higher responses, in all the analyzed aspects, toward the dose pulsed to 20%, confirming its therapeutic properties related to the initial phases of tissue healing.