Aerial images contain a lot of geographical information. They are important data sources for GIS. But, because of environment elements' affection, their contrasts are often low and illumination is not equal. So image enhancement becomes an important problem in aerial image processing. According to the gray feature of aerial images, this paper presents a method for fuzzy enhancement to improve the image contrast. The method includes the following three steps. First, the relative gray of a pixel is used as a fuzzy feature. So an image is translated into fuzzy sets. Second, a kind of fuzzy enhancement operator is used to the fuzzy sets. Through the fuzzy enhancement operator, new ehnanced fuzzy sets are formed. Third, the new enhanced fuzzy sets are translated reversely into a new gray image. The gray image is the enhanced image. Experimental results show that the method of fuzzy enhancement is better than the conventional methods. In addition, the method also enhances special objects in accord with needs.