Spent potliners (SPL) is solid waste generated by the aluminum industry during the manufacture of aluminum metal. Information on the cytotoxicity effect of SPL is necessary to facilitate understanding of their action on organisms and to subsidize environmentally correct solutions. Thus, the aim of the present investigation is to compare the effect of SPL on meristematic cells of Allium cepa and Zea mays and also to discuss the mechanisms of SPL cytotoxicity involved. A strong inhibition on root growth in higher SPL concentrations has been observed in both A. cepa and Z. mays. For cytogenetic analysis, the results showed a reduction of mitotic index and increase of different abnormalities as the SPL concentration increased. We observed bridges, chromosome fragments, stickiness, multipolar anaphase, later segregation and cell death. In general, it was possible to observe an increase of different abnormalities as the SPL concentration increased. It is obvious from the results of the present investigation that SPL is cytotoxic on meristematic cells of plant tests ( A. cepa and Z. mays).