Simple SummaryLife history and its related theories are one of the most important topics in behavioral ecology, population ecology, and evolutionary biology. The reproductive ecology of birds is the cornerstone of avian life-history theory, and the success or failure of reproduction directly affects the survival and development of the population. This study investigated the reproductive ecology of chestnut-vented nuthatch (Sitta nagaensis) using artificial nest boxes to attract these secondary cavity-nesting birds. The study focused on a series of breeding activities and is the first breeding record ofS. nagaensisin southwestern China, providing a basis for further reproductive ecology studies of this species.AbstractThe breeding ecology of birds is the cornerstone of bird life-history theory, and breeding success directly affects the survival and development of populations. We studied the breeding ecology of a secondary cavity-nesting bird, the chestnut-vented nuthatchSitta nagaensis, in southwestern China from March to June in 2020, 2021, and 2022. In total, 16 nests in nest boxes and 19 nests in natural cavities were studied. The nesting habitat was mainlyPinus yunnanensisforest (68.4%), and the nest trees were mainlyP. yunnanensisand pearPyrusspp. Cavities made by woodpeckers and knot holes were used as nest sites, and the nuthatches plastered the hole entrance with mud. The nesting material was mainly pine bark. The clutch size was 3.47 ± 0.56 (range 2–4,n= 30), with an incubation period of 16.06 ± 0.91 days (range 15–19 days,n= 18). The nestling period was 20.88 ± 1.90 days (range 18–23 days,n= 23), and both parents fed the nestlings.