WO3 nanosheets were synthesized by an acidification method and Cr was loaded on the surface of nanosheets via an impregnation procedure. The morphologies of pristine and Cr-loaded WO3 nanosheets were analyzed. Gas sensors based on pristine and Cr-loaded WO3 nanosheets were fabricated by a screen-printing technique and their sensing properties were also investigated. It was found that the catalytic modification of Cr can significantly improve the sensing performance of WO3 nanosheets to ammonia. In addition, the sensitization mechanism of Cr-loaded WO3 could be caused by the electrical sensitization effect and more stable product in the sensing processes to ammonia.