Background: Alterations in the sleep-wake cycle leads to decreased melatonin secretion and it may be associated with sleep disorders and cancer risk. Exposure of light at night and rotating night shift decrease the melatonin production due to acute suppression of pineal melatonin secretion during night work has been suggested to increases cancer risks. Aims & Objectives: The objectives of the present study were to investigate the effect of light exposure at night on circadian pattern of 6-Sulfatoxy melatonin levels in night shift nursing professionals. Material and Methods: 62 healthy nursing professionals of both genders performing day and night shifts (continuous 9 days night shift with alternate day shifts) were recruited. Urine samples were collected at around 8 hour intervals (afternoon sample: between 13:00 to 15:00, night samples between 22:00 to 01:00 and morning samples between 05:00 to 08:00) while they were performing night duties and repeated when they were assigned day duties. Night melatonin level was decreased as compared to morning melatonin. Results: Night melatonin level was found declined as compared to morning level and this pattern was significant when compared night melatonin between night (16.71 ± 11.98) vs day shift (22.71 ± 13.25) and morning melatonin level between night (20.07 ± 14.13) vs day shifts (28.26 ± 14.14) (p<0.001). Conclusion: Light exposure at night disrupts the circadian rhythm of melatonin secretion during night shift leads to internal desynchronization.