Walking behavior in rainy conditions is very different from that without rain. This paper aims to study the effects of rainfall intensity on pedestrian walking behavior at signalized crosswalks. In the paper, fundamental diagrams such as speed-flow relationships are calibrated in various rainy conditions. The impacts of rainfall intensity on the reduction of walking speed are empirically investigated. Controlled experiments are conducted to collect pedestrian data such as walking speed, flow, bi-directional flow ratio in both no-rain and rain conditions. A generalized pedestrian speed-flow function is proposed and calibrated, taking into account the effects of varied rainfall intensity. The generalized speed-flow function is useful for evaluating the performance of pedestrian facilities, particularly in Hong Kong and other Asian cites with relatively high annual rainfall intensity. The findings could provide better insights into the effects of rainfall intensity on pedestrian walking behavior for assisting engineers/planners in improving the design and operation of pedestrian facilities.