To provide a composition of a non-discoloring grease base oil diffusion preventing agent having a base oil diffusion preventing effect; and a grease comprising the same.

The grease base oil diffusion preventing agent contains a perfluoroalkyl group-containing polyoxyalkylene compound (A) represented by general formula (1): B-A-OB (wherein A represents a polyoxyalkylene group containing a 1-30C perfluoroalkyl group (the alkylene group has 1 to 4 carbon atoms), or represents a polyoxyalkylene group substituted with wholly or partially fluorinated alkyl groups (the alkylene group has 1 to 6 carbon atoms), and B represents a hydrogen atom, a 1-5C acyl group, or a 1-10C non-fluorinated alkyl group).