UV photodetector have been successfully implemented in various applications like ozone sensing, communication, astronomy and flame detection etc. Zn(Mg)O is a wide band gap material with high excitonic binding energy at room temperature thus making it a promising material in optoelectronic industries. In the present work, we are achieving increased photocurrent and high responsivity in UV-A regime with post growth UV-ozone treatment from photodetector fabricated using RF sputtered ZnMgO thin film. The thin film was deposited on semi-insulating silicon wafer at 400C for 20 min followed by 70 min UV-Ozone treatment. The final step was to fabricate an interdigitated electrode on the processed samples. More than two times enhancement of photocurrent was observed after UVO treatment. Noteworthy responsivity values of 22 A/W and 67 A/W were measured from as-deposited and UVO annealed photodetector, respectively at 380 nm with an applied bias of -5 V bias. However, the measured detectivity values for as grown and UV-O annealed sample was 1.3 × 10<sup>13</sup> and 2.7 × 10<sup>13</sup>, respectively. Noise equivalent power in as-deposited sample and UVO treated sample was estimated to be 2.4 × 10<sup>-12</sup> W/√Hz and 1.1 × 10<sup>-12</sup> W/√Hz respectively. Photo detector fabricated with UV-O annealing exhibited good switching behaviors with 37 ms and 30 ms rise and fall time, respectively.