Xinchengzi is a town in the Miyun District of Beijing, China. It lies in the northeastern part of the municipality, in a mountainous area near the border with Hebei province.
The town is bordered by Liangjianfang and Laowa Townships to the north, Wulingshan Town to the east and south, and Gubeikou and Taishitun Towns to the west. As of 2020, it had a population of 6,528 residents under its administration.
Xinchengzi is one of several towns and townships that make up the rural and semi-rural periphery of Miyun District, an area known for its reservoir and mountainous terrain rather than for dense urban development.