Abstract: A bauxite ore in Chongqing is mainly composed by the sedimentary type diaspore，boehmite and gibbsite，silicon to aluminum ratio is 5.19.Direct-flotation test were conducted by Institute of Multipurpose Utilization of Mineral Resources，Chinese Academy of Geological Sciences using self developed collector EM505 with grinding fineness of 75% -0.074 mm，via two roughing and three cleaning，rough concentration tailing and cleaning tailings mixed and via one scavenging and one cleaning process，concentrate with Al₂O₃ grade of 68.86%，SiO₂ grade of 6.79% and with the recovery of Al₂O₃ 83.39%，and silicon to aluminum ratio of 10.14 was obtained，which can be used in production of Bayer method.Synchronous flotation of both coarse and fine particles was achieved by using the collector EM505.At the same time，the flotation concentrate bubble is brittle，small and fast speed of merger and mineralization by use this collector，especially not sticky，so the collector EM505 is a high efficient collector for direct-flotation on bauxite.

Key words: EM505 collector, Diaspore, Direct flotation