In this study, we investigated the photoelectric properties of nanosized anatase (∼55 and ∼4 nm) under high pressure, utilizing in situ Raman spectroscopy, photocurrent measurements, and theoretical calculations up to 27.6(5) GPa. Our findings reveal that 55 nm anatase shows a significant photocurrent increase of 2.4 times compared to ambient conditions before transitioning to the columbite phase at around 5.5(1) GPa. After this transition, the photocurrent gradually decreased up to 19.8(4) GPa. Notably, the columbite phase exhibited superior optoelectronic performance compared to the baddeleyite phase observed at approximately 15.5(3) GPa. For ∼4 nm anatase, an exceptional photocurrent increase of approximately 131 times was observed at 5.4(1) GPa compared to 1.5(0) GPa, with only a slight decrease between 5.4(1) and 27.6(5) GPa, and maintained a high level even after pressure release. The observed variations in photocurrent are attributed to changes in resistance, band gap, and absorption coefficient, each influencing the material’s response differently across various pressure ranges. These results underscore the potential of pressure-induced modulation to dramatically enhance the photoelectric properties of nanosized anatase, especially in ∼4 nm anatase. The ability to control the crystal structure and UV light response through pressure offers a promising strategy for improving the performance of TiO₂-based ultraviolet photodetectors, making them more effective for advanced photoelectric applications.