Nowadays, more and more power equipment has begun to use new insulation paper to replace traditional cellulose insulation paper, along with new oil insulation structures, to ensure its’ applicability in more extreme environments. Nomex insulation paper boasts better mechanical and electrical properties than conventional cellulose insulation paper, and it can operate stably at higher temperature for a longer lifetime without significant loss of insulation properties. In this paper, we measured the DC conductivity and AC/DC breakdown field strength of Nomex paper and Kraft paper immersed in KI25X insulation oil. Additionally, the infrared spectra of both types of paper were tested and analyzed. The results indicate that the AC and DC breakdown field strength of Nomex insulation paper is lower than that of Kraft insulation paper. However, the DC conductivity of Nomex insulation paper is significantly lower than that of Kraft paper, and the chemical stability of Nomex insulation paper is notably higher than that of Kraft insulation paper. This proves that Nomex insulation paper possesses better electrical properties and is more suited for insulation oil-immersed transformers.