The objective of this work is to evaluate the action of original Roundup® on the snail Biomphalaria glabrata infected and not infected by Schistosoma mansoni by observing its mortality and reproductive biology. Snails were submitted for 30 days to aqueous solutions of original Roundup at concentrations of 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, 0.018, 0.016, 0.014, 0.012 and 0.01 (%) to determine LC50. To analyze the reproductive activity of B. glabrata, against the pesticide, four B. glabrata groups were formed: infected and exposed to the pesticide; infected and not exposed (control); not infected and exposed; and not infected and not exposed(control). LC50 (0.012% aqueous solution of original Roundup) caused mortality of at most up to 95% for 24, 48 and 72 h during the experimental period (30 days), and lost effect totally after 27 days. The reproductive activity of the non-infected and exposed snails was 30.3 ± 20.5 eggs in 2.7 ± 1.2 egg masses, and there was a reduction of 51% in the average number of hatched snails (11.5 ± 7.5) in comparison to the control group (23.9 ± 18.0) for four weeks (p = 0.003). The results indicate that the lethal concentration (LC50) of the 0.012% aqueous solution of original Roundup has a significant action on Biomphalaria glabrata for up to 27 days. Roundup significantly diminished the fertility of infected and exposed snails in comparison with the control group.