The 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 nuthatch Sitta 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 mainly Pinus yunnanensis forest (68.4%), and the nest trees were mainly P. yunnanensis and pear Pyrus spp. 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.