A brightness enhancement film (BEF) including a first surface, a second surface, and a side surface is provided. The first surface is a curved surface continuously fluctuant in two dimensions and includes a plurality of axisymmetric convex surfaces and a plurality of non-axisymmetric concave surfaces. Each of the axisymmetric convex surfaces is a curved surface. The axisymmetric convex surfaces and the non-axisymmetric concave surfaces are arranged alternately in the two dimensions and respectively form a plurality of wave crests and a plurality of wave troughs. Each of the non-axisymmetric concave surfaces is a curved surface. The second surface is opposite to the first surface and the side surface connects the first surface and the second surface. In addition, a backlight module employing the BEF is also provided.