AbstractBackground: Many modern lifestyles are unhealthy andcan negatively affect our health. Many studies showed thatthe stress caused pronounced action on the structure of variousbody systems. The liver is one of the body organs that can beheavily affected by stress. The liver can withstand stress forlonger periods and shows signs of damage very late althoughthe structural changes can be detected very early.Aim of Study: Is to examine the acute and chronic effect of acute and chronic stress of long-term continuous light exposure on the structure of the liver tissues.Material and Methods: 48 male and female Wistar rats (250-300g) were enrolled in 6 groups (n=8/group). Group (a);Normal male control group with normal light/dark exposure.Group (b); Normal female control group with normal light/darkexposure. Group (c); Continuous room light for 3 weeks malegroup as an acute stress model in which normally fed malerats exposed to continuous room light exposure for 3 weeks.Group (d); Continuous room light for 3 weeks female groupas an acute stress model in which normally fed female ratsexposed to continuous room light exposure for 3 weeks.Group (e); Continuous room light for 3 months male groupas a chronic stress model in which normally fed male ratsexposed to continuous light exposure for 3 months. Group (f); Continuous room light for 3 months female group as achronic stress model in which normally fed female rats exposed to continuous light exposure for 3 months.Results: Sections of liver tissues of the groups who livedunder acute stress showed generally, preserved hepatic archi-tecture. The hepatocytes showed marked ballooning (vacuolardegeneration). The sinusoids and central veins showed con-gestion. Sections of liver tissues of the groups who livedunder chronic stress conditions showed in general, preservedhepatic architecture. The hepatocytes showed ballooning (vacuolar degeneration), focal spotty necrosis, together withsome binucleated cells. The sinusoids & central vein showedcongestion.Conclusion: This study used 48 Wistar mice as a modelto assess the effect of stress on liver tissues. Continuous roomlight exposure was used as acute stress for 3 weeks and aschronic stress for 3 months. This stressful stimulus and its deleterious effect on the liver may be supported by the theoryof sympathetic nervous system overactivity. The examinedliver tissues in this study showed congestive and degenerativechanges both in acute and chronic stressed animals. Changingmodern lifestyles to one that respects the natural chronobiologyis important for our wellbeing.