The conservation of songbird migrants in China faces challenges similar to those in other parts of the world such as Europe and North America. Songbird migrants have complex life history and are associated with large spatial scale. The events occurred during migration play a critical role in determining population status. Little is known about stopover behavior of migratory songbirds in China during passage, including stopover duration, energetic condition (e.g., the amount of fat stores), and habitat use of these birds. We investigated migration timing, stopover duration, change of energetic condition, and sex-related variations among Red-flanked Bush Robin (Tarsiger cyanurus) at a stopover site in northeast China. A total of 1,751 and 684 Red-flanked Bush Robins were captured in fall 2002 and in spring 2003, respectively. Body mass of fall birds was higher than that of spring birds. Condition index (i.e., body mass adjusted for body size) was lowest among spring females. Birds were more likely to stay longer in fall than in spring. We detected a positive relationship between time of initial capture and condition index regardless of season or sex, suggesting birds were able to replenish energy stores. The net daily mass gain was the highest among males in fall (3% body mass). The net daily mass gain would sustain a flight of 0.6 h for females and 3.1 h for males in fall. The stopover biology of Red-flanked Bush Robins is similar to some songbird migrants of Europe and North America. For example, spring passage time and fat store variation between sexes agree with the hypothesis that males are selected to arrive at their breeding grounds as early as food resources or climatic conditions are adequate in spring. Further research on stopover ecology is urgently needed in China for a better understanding of the migratory behavior and for the conservation of these songbird migrants.