Objective To detect 25% cyhalofop-butyl emulsifiable concentrate(EC) skin sensitization by a local lymph node assay (BrdU-ELISA) in mice. Methods Female BALB/ C mice were tested and the samples were set up to 100%, 50%, and 25%. The negative control group received acetone: olive oil (AOO)= 4 ∶1, and the positive control group received 25% basal cinnamaldehyde. Test samples were laid on the dorsum of bilateral mouse ears for three consecutive days, then the mice received an intraperitoneal injection of BrdU (5 mg/ mouse) on the sixth day. After 24 hours, the lymph nodes were removed, weighed, and mashed into a cell suspension. Lymphocyte proliferation was measured by BrdU-ELISA. Results The body weights of female mice in all treated groups were similar to the control group. The increase of ear thickness and ear weight in each dose group was not more than 25%. The stimulus indexes of solvent and blank control groups were SI₁and SI₂< 1. 6, and the stimulation indexes of the positive control group (25% hexyl cinnamaldehyde) were SI₁and SI₂ > 1. 6. This indicated the test system was reliable. The stimulation indexes of 25%cyhalofop-butyl EC in the low, medium and high dose groups were SI₁and SI₂ < 1. 6, and there was no dose-response relationship. Conclusions The results of 25% cyhalofop-butyl EC in mouse local lymph node assays were negative,indicating that 25% cyhalofop-butyl does not cause skin sensitization.