Detection of nucleobases is of great significance in DNA sequencing, which is one of the main goals of the Human Genome Project. The synthesis of Hachimoji DNA, an artificial genetic system with eight nucleotide bases, has induced a transformative shift in genetic research and biosensing. Here, we present a systematic investigation of the adsorption behavior and electronic transport properties of natural and modified DNA bases on a Janus molybdenum sulfur hydride (MoSH) monolayer using density functional theory (DFT) and nonequilibrium Green’s function (NEGF) methods. Our results demonstrate that the S side of the MoSH monolayer is more effective as a sensing platform compared to the H side, which undergoes significant structural distortions due to chemisorption. The S side selectively distinguishes natural bases A and T from G and C, and modified bases S and Z from others. However, the negligible changes in current after base adsorption highlight the limitations of relying solely on current sensitivity for detection. Our findings provide valuable insights into the design of MoSH monolayer-based sensing platforms for selective DNA base detection, with potential applications in next-generation DNA sequencing technologies.