Algal extracts are sources of bioactive substances with applications in the development of novel alternative drugs against several diseases, including trichomoniasis sexually transmitted infection caused byTrichomonas vaginalis. Factors such as clinical failures and resistant strains limit the success of the existing drugs available for treating this disease. Therefore, searching for viable alternatives to these drugs is essential for the treatment of this disease. The present study was conducted for,in vitroandin silicocharacterization of extracts obtained from marine macroalgaeGigartina skottsbergiiat stages gametophidic, cystocarpic, and tetrasporophidic. In addition, antiparasitic activity of these extracts against the ATCC 30236 isolate ofT.vaginalis, their cytotoxicity, and gene expression of trophozoites after treatment were evaluated. The minimum inhibitory concentration and 50% inhibition concentration were determined for each extract. Results:In vitroanalysis of the extracts’ anti-T.vaginalisactivity revealed an inhibitory effect of 100%, 89.61%, and 86.95% forGigartina skottsbergiiat stages gametophidic, cystocarpic, and tetrasporophidic, respectively, at 100 μg/mL.In silicoanalysis revealed the interactions between constituents of the extracts and enzymes fromT.vaginalis, with significant free energy values obtained for the binding. None of the extract concentrations exhibited cytotoxic effects on VERO cell line compared to control, while cytotoxicity on HMVII vaginal epithelial cells line was observed at 100 μg/mL (30% inhibition). Gene expression analysis revealed differences in the expression profile ofT.vaginalisenzymes between the extract-treated and control groups. According to these results,Gigartina skottsbergiiextracts exhibited satisfactory antiparasitic activity.