Purpose - In order to replace the conventional human maintenance of cable-stayed bridges, a robot is designed and constructed for tasks such as cleaning, painting and rust-detecting. Design/methodology/approach - Adopting a modular approach, two kinds of climbing mechanisms, plus a painting mechanism and a rust-detecting method are designed. Findings - A robot that can climb and maintain the cables of cable-stayed bridges has been designed and constructed. It has been proved by experiment that the robot can overcome many disadvantages of conventional human bridge-maintenance, and drastically improve efficiency, cost, and safety. Research limitations/implications - The robot is of industrial size, but a new mechanism requiring less installing time will be designed for the future. Practical implications - The robot has been applied to cables of the Nanpu Bridge and Xupu Bridge in Shanghai. More than 80 cable-stayed bridges and six suspension bridges have been built or are being constructed across large rivers in China alone. This gives an enormous potential market. Originality/value - The cable maintenance robot developed in this paper is the world's first special robot for the cables of cable-stayed bridges.