The monitoring of phytochemicals with potentially toxic properties can be assessed by observing the physiological and cellular alterations of the test organism exposed. This present study aimed to evaluate the cytotoxic and genotoxic potential of aqueous extracts of leaves and roots of Macroptilium lathyroides weed on the cell cycle of lettuce. Bioassays were conducted in a germinator (25 oC) with aqueous extract at concentrations of 0, 5, 10, 20 and 40% p v-1, obtained from fresh leaves and roots. For biological, lettuce root meristems were used for the preparation of slides using the technique of squashing. All blades were observed with an optical microscope at a magnitude of 400x. A total of 5,000 cells were analyzed for each treatment, and the number of cells in each phase of mitosis was recorded. Possible presence of chromosomal abnormalities was verified, such as chromatid breaks, anafasic bridges, loss of whole chromosomes or micronuclei formation. These analyzes were conducted only on a qualitative level. Results showed that aqueous extracts of M. lathyroides mitotic caused reduced index with increased concentration. Genotoxic activity was also observed for both extracts tested, since composition resulted in cell cycle changes and chromosomal abnormalities.