Cirsium ehrenbergii ("red thistle") is a folk medicinal plant of the state of Hidalgo, Mexico. Its flowers and roots are used to prepare an infusion for drinking or applying vaginal douches; nevertheless, neither its secondary metabolites nor therapeutic properties have been described or confirmed. Flowers of C. ehrenbergii, were collected, dried and milled. Aqueous, methanol and hexane extracts were carried out by maceration to obtain polar and non-polar secondary metabolites. The presence of alkaloids was determined by Wagner, Mayer and Dragendorff techniques; both polar and non-polar extracts yielded positive results. Toxicity was quantified by the Artemia salina mortality method, the aqueous extract showed moderate toxicity, while methanol and hexane extracts yielded a very similar and high concentration-dependent mortality. Antibacterial activity was evidenced by cellular growth inhibition of six bacterial strains, wherein the aqueous extract was inactive; the methanol extract was almost ineffective, while the hexane extract showed a high concentration-dependent antibacterial activity on all strains. An isolated organ study was performed with rings of uterus from estrogen-treated female Wistar rats to evaluate relaxing effects on uterine smooth muscle. Rings were pre-contracted with KCl (60 mM). The methanol extract inhibited contraction modestly at the highest concentration (300 pg/mL). The hexane extract markedly inhibited contraction in a concentration-dependent manner. The hexane extract was biologically more effective than the methanol extract. The traditional use of C. ehrenbergii as a medicinal plant may be supported by pharmacological actions.