DNA methylation is a critical epigenetic modification that regulates gene expression, maintains genome stability, and influences cellular function during development and disease. Accurate analysis of DNA methylation often requires amplification to generate sufficient material, yet preserving the original epigenetic information during this process is challenging because standard amplification methods can disrupt methylation patterns. To address this, we developed a one-pot strategy that combines helicase-dependent amplification (HDA) with DNA methyltransferase 1 (DNMT1)-mediated methylation, enabling simultaneous DNA amplification and preservation of native methylation marks. A key challenge is that HDA is optimized at 65 degree Celsius, whereas DNMT1 is unstable at elevated temperatures. We overcame this by establishing a unified buffer and isothermal reaction at 42 degree Celsius that supports both enzymatic activities. Under these conditions, HDA achieved robust amplification (~5 Ct), while DNMT1 faithfully methylated the newly synthesized DNA, as confirmed by methylation-sensitive restriction enzyme quantitative PCR (MSRE-qPCR), with methylation levels proportional to the input template. This one-pot workflow demonstrates the feasibility of concurrent amplification and methylation, providing a foundation for scalable, accurate, and methylation-preserving DNA analyses for epigenetic and clinical applications.