In this study, the genotoxic effects of the herbicide trifluralin on the root meristem cells of sunflowers (Helianthus annuus L.) were investigated. The roots were treated with 5 10, 20 and 40 parts per thousand concentrations of trifluralin for 24, 36 and 48 h, with a control for each combination. The morphological changes occurring in sunflower roots with the different herbicide concentrations were monitored. The mitotic index and mitotic abnormalities were determined in both control and test groups. Mitotic index decreased with increasing herbicide concentration at each exposure time. The mitotic abnormalities were recorded as disturbed prophase, c-mitosis, stickiness, laggards and chromatid bridges. The micronucleus was observed at interphase and its frequency was calculated in different test solutions. Thus, the genotoxic potency of trifluralin with different tests was assessed by using root tip cells of Helianthus annuus.