An object of the invention is to provide a grease composition, having enough low-dust generation property for using thereof in a clean environment, for example, a clean room, and having enough load bearing in order to lubricate a motion guiding device to be incorporated in a large-scale of clean robot. The grease composition for a clean environment comprising, a base oil, a thickener and a extreme-pressure agent, in which a kinetic viscosity of the base oil at 40°C is 100~300 mm 2 /s, the thickener comprising a lithium complex soap, a content of the thickener is 10~40 mass% with respect to the total amount of the grease composition.