A diffuser includes a body and diffusion blades disposed at a circumferential edge of the body. The body includes an air inlet side and an air outlet side. Each diffusion blade has an inclined guide surface. The guide surface has a starting end at the air inlet side of the body and a terminating end adjacent the air outlet side of the body. The guide surface extends from the starting end to the terminating end along a circumferential path and has a width gradually increasing from the starting ending to the terminating end. The diffuser further includes air outlets at the terminating ends of the guide surfaces. Each air outlet fluidly connects the terminating end of a corresponding one of the guide surfaces and the air outlet side of the body. A blower employing the diffuser is also provided.