Abstract: Flumioxazin, which targets the protoporphyrin oxidase, is an N-phenylphthalimide herbicide. In order to explore its application prospect in cotton fields of China, the weed controlling spectrum, herbicidal activity and safety of flumioxazin to cotton were tested under greenhouse conditions. The results showed that flumioxazin displayed good controlling effect on the common broadleaf weeds infesting cotton. At the rate of 15 g a.i./hm2, flumioxazin application resulted in higher than 90% fresh weight reduction of Portulaca oleracea, Amaranthus retroflexus, Chenopodium album, Chenopodium serotinum and Eclipta prostrate, and 80%-90% fresh weight reduction of Rorippa indica, Sonchus arvensis, Conyza canadensis, Solanum nigrum, Digitaria sanguinalis and Eleusine indica. Flumioxazin showed higher herbicidal activity against P. oleracea, A. retroflexus, S. nigrum, C. album than pendimethalin. The selectivity indexes between Lumianyan 28 and P. oleracea, A. retroflexus, S. nigrum and C. album were 79.1, 38.1, 32.1 and 112.6, respectively, which were much higher than that of pendimethalin with corresponding selectivity index of 12.0, 9.9, 5.8 and 9.2, respectively. The selectivity index between Lumianyan 37, Xinqiu 4 and the weed species mentioned above was similar to that of Lumianyan 28. This study indicated that the flumioxazin could be used as one of candidate herbicides for the control of broadleaf weeds in cotton fields.