This paper describes a novel mechanism with passive crawlers that will realize a stair-climbing rescue robot with simple system. The proposed mechanism is called “SMART-III”, it is named after “Simple Mechanism Adaptive for Rough Terrain”. Some quasi-static dynamic analysis were implemented and effectiveness of limitation for crawler rotation angle were verified. A prototype robot with the SMART-III mechanism had been improved. Experimental results show the effectiveness and performance of the proposed mechanism against a step and continuous stairs.