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Light interaction physical properties of MXenes are fundamentally important and promising for developing new broadband photodetection applications. In this work, the significant influence of intercalants on the photo‐electronic properties of MXenes is studied. It is found that the intercalated H2O‐induced inter‐flake resistance greatly restricts the photon excitation responsivity of Ti3C2Tx, resulting in a slow and irreversible resistance change under laser irradiation. After deintercalation of H2O by in situ laser writing, the resistance of Ti3C2Tx responds fast and reversibly to laser excitation and the variation range is proportional to laser power. By extending the findings to another MXene member, Mo2TiC2, the intercalant induced resistance is successfully developed for optoelectronic detection. By selectively deintercalating H2O in the as‐prepared Mo2TiC2 which is co‐intercalated by H2O and TMAOH, bare TMAOH intercalated Mo2TiC2 shows fast and reversible resistance changes with laser. Moreover, the resistance of bare TMAOH intercalated Mo2TiC2 shows a negative temperature coefficient behavior while the fully deintercalated Ti3C2Tx shows a positive temperature behavior. These findings elucidate the understanding of the optoelectronic properties of MXenes and provide insights into the engineering of interfacial chemistry of MXenes for performance enhancement toward various detectors/sensors beyond optoelectronic applications. [ABSTRACT FROM AUTHOR]