Cobalt,iron,and selenium in rocks,soils,and forage plants,of six background zones different in geology in the major ruminant product ion base of Yunnan were determined and analyzed.Results show that in terms of abundance of cobalt,iron,and selenium in soil and forage,the Paleozoic Basalt Zone(Ⅴ) and Carbonate Red Earth Zone(Ⅰ),are at the top,the Yellow Red Earth Zone of mixed of Carbonate,Clastic Rock and Basalt(Ⅱ) in the middle and the Purple Earth Zone of Mesozoic Clastic Rock(Ⅲ),the Yellow Red Earth Zone of Clastic Rock(Ⅳ),and the Dark Red Earth Zone of Precambrian Metamorphic Rock(Ⅵ),at the bottom.The concentrations of cobalt,iron,and selenium in forages are affected by the geological background values,especially abundances of these microelements in the soil.