In this paper, a novel adaptive soft morphological gradient (ASMG) filter is proposed, based on a combination of the idea of the soft morphological filtering and the adaptive technique. ASMG filtering is an efficient nonlinear sharpening method, which can be applied for edge detection. By employing four directional structuring elements, ASMG filtering has the capability of selecting the directional structuring element with the maximum response, whose direction varies depending on the change of directional edges. In addition, by comparing the variance of the moving structuring window with the base variance, the ASMG filter provides an adaptive algorithm for morphological operations. The experimental results show that the ASMG filter is better than the traditional operators in edge detection and noise suppression.