In this research, the genotoxic and cytotoxic effects of the insecticide deltamethrin (DEL) on the root meristem cells of sunflowers (Helianthus annuus L.) were investigated. The lethal dose (LD50) value was determined as approximately 1 ppm in the sunflower root growth tests. The roots were treated with 1 (LD50), 0.25 (LD50 /4), 0.5 (LD50/2) and 2 ppm (LD50 x2) concentrations of DEL for 24, 36 and 48 h, with a control for each combination. Occurring morphological changes such as reduction of root elongation and discoloration in sunflower roots were observed with the using DEL concentrations. The mitotic index and mitotic abnormalities were determined in both control and test groups. Mitotic index reduced with increasing the insecticide concentration at each exposure time. The mitotic abnormalities were recorded as disturbed prophase, c-mitosis, stickiness, laggards and chromatid bridges. In addition, micronucleus was observed at interphase and its frequency was calculated in the test solutions.