In the context of the widespread integration of artificial intelligence (AI) technology into education, this study aims to understand the factors influencing Vietnamese mathematics teachers' adoption of ChatGPT in secondary school teaching. Based on the Unified Theory of Acceptance and Use of Technology model, the study uses a quantitative approach with data collected from 490 teachers. It applied the Partial Least Squares Structural Equation Modeling to examine factors influencing this adoption. The results indicate that Performance Expectancy (PE), Effort Expectancy (EE), Social Influence (SI), and Perceived Trust (PT) significantly affect teachers' Behavioral Intention (BI) to incorporate ChatGPT into their instruction. The study also examines the influence of moderator variables, such as geographic location and gender. While PE, SI, and PT significantly impact BI, no statistically significant differences were found between urban and rural teachers. In contrast, gender differences emerged: PE had a more substantial effect on females, SI influenced males and females differently, PT was significant only for males, and EE impacted only females. Most of these results align with existing research on AI adoption in education. To implement ChatGPT effectively, the study introduces a structured training program aimed at helping teachers integrate ChatGPT into their classrooms. Despite its theoretical and practical contributions, this study has certain limitations and suggests directions for future research. Further studies could incorporate qualitative methods to gain deeper insights, employ random sampling techniques with more extensive and diverse samples to enhance generalizability and explore additional constructs within the theoretical model to provide a more comprehensive understanding of AI adoption in education.