Abstract: A new approach to radiation source imaging with a rotating edge was proposed. Differentiating the edge response curve can yield the integration of the emission intensity of the source along the direction of the edge, which is similar to the projection of a source in CT technology. Multiple projections from different directions can be obtained by rotating the edge, from which the distribution of source intensity can be reconstructed. A tungsten alloy step edge was used in the imaging experiment on a 60Co gamma source. The image of the active region of the source could be reconstructed from the edge responses of 400 projections, indicating this new approach is feasible. It can be applied to measure the size of small radiation sources, such as the focus of an X-ray generator, using a step edg