Background: Native bees of the tribe Meliponini produce a distinct kind of propolis called geopropolis. Although many pharmacological activities of propolis have already been demonstrated, little is known about geopropolis, particularly regarding its antimicrobial activity against oral pathogens. The present study aimed at investigating the antimicrobial activity ofM. fasciculatageopropolis against oral pathogens, its effects onS. mutansbiofilms, and the chemical contents of the extracts. A gel prepared with a geopropolis extract was also analyzed for its activity onS. mutansand its immunotoxicological potential.Methods: Antimicrobial activities of three hydroalcoholic extracts (HAEs) of geopropolis, and hexane and chloroform fractions of one extract, were evaluated using the agar diffusion method and the broth dilution technique. Ethanol (70%, v/v) and chlorhexidine (0.12%, w/w) were used as negative and positive controls, respectively. Total phenol and flavonoid concentrations were assayed by spectrophotometry. Immunotoxicity was evaluated in mice by topical application in the oral cavity followed by quantification of biochemical and immunological parameters, and macro-microscopic analysis of animal organs.Results: Two extracts, HAE-2 and HAE-3, showed inhibition zones ranging from 9 to 13 mm in diameter forS. mutansandC. albicans, but presented no activity againstL.acidophilus. The MBCs for HAE-2 and HAE-3 againstS. mutanswere 6.25 mg/mL and 12.5 mg/mL, respectively. HAE-2 was fractionated, and its chloroform fraction had an MBC of 14.57 mg/mL. HAE-2 also exhibited bactericidal effects onS. mutansbiofilms after 3 h of treatment. Significant differences (p < 0.05) in total phenol and flavonoid concentrations were observed among the samples. Signs toxic effects were not observed after application of the geopropolis-based gel, but an increase in the production of IL-4 and IL-10, anti-inflammatory cytokines, was detected.Conclusions: In summary, geopropolis produced byM. fasciculatacan exert antimicrobial action againstS. mutansandC. albicans, with significant inhibitory activity againstS. mutansbiofilms. The extract with the highest flavonoid concentration, HAE-2, presented the highest antimicrobial activity. In addition, a geopropolis-based gel is not toxic in an animal model and displays anti-inflammatory effect.