Plant litter is not only the major source of carbon (C) and nutrients for heterotrophic organisms in forest headwater streams, but also an important component of stream C storage. The dynamics of stream litter storage (i.e., the standing stock) are thus closely related to forest C fluxes, but has not been well assessed in the literature. To fill this gap, we investigated the monthly dynamics of plant litter storages at 17 reaches of a subtropical headwater stream from stream source to mouth during the rainy season (from March to August) of 2021. We found that (1), across sampling reaches, the mean litter storages of leaves, twigs (< 1 cm in diameter), fine woody debris (FWD, < 10 cm in diameter), reproductive parts (flowers and/or fruits), and barks in the stream during the rainy season were 25.6, 11.9, 16.7, 0.3, and 0.6 g/m², respectively, and the storage peak of total litter was in May, while the storage peaks at most of the sampling reaches were in April and May; (2) litter storage, especially leaf litter, at the stream source reach (i.e., reach 1) was significantly higher than those in the other reaches, and riparian forest type affected the storages of twig and FWD litter, with higher values in reaches with broad-leaved than mixed riparian forests; and (3) stream physicochemical characteristics, especially channel gradient, channel width, and water discharge and alkalinity, had significant effects on litter storage, but their effects varied among different litter types. Overall, our study clearly assessed the dynamics of plant litter storages in a headwater stream of subtropical forests, which will help us to better understand the role of headwater streams in forest carbon storage and cycling.