Previous research has demonstrated that visual properties of objects can affect shape-based categorization in a novel-name extension task; however, we still do not know how a relationship between visual properties of objects affects judgments in a novel-name extension task. We examined effects of increased visual similarity among the target and test objects in a shape bias task in young children and adults. Experiment 1 assessed college students with sets of objects whose similarity between target and test objects was either low or high similarity. Adults preferred shape when the similarity among objects was minimized. Experiment 2 tested 24-month olds in their use of the shape bias using the Intermodal Preferential Looking Paradigm. Children showed a shape bias only with items whose similarity to each other was low. These findings suggest that the visual properties of objects affect shape bias performance. (Contains 4 figures.)