The crowding effect refers to the fact that observers' ability to recognize an object in the periphery deteriorates when the target object is flanked by other items, especially if the target and flankers are similar. Here, a reduction of the crowding effect was caused by a topological difference between target and flankers. In three experiments using a number of different stimulus patterns (e.g., triangles and arrows; digits and letters and geometrical shapes), results showed that the crowding effect was significantly reduced when the target and the flankers were topologically different. Control experiments showed that such a reduction of the crowding effect was not due to differences in subjective similarity, or differences in geometrical features such as area and shape. This finding suggests that topological properties play an important role in perceptual grouping which influences the crowding effect.