The metabolic process follows a circadian rhythm. Circadian rhythm is influenced by changes in the light/darkness cycles. One of these metabolic processes have to do with lipid synthesis. Lipidic profile quantifies this synthesis. This research was conducted in order to determine the variation of lipidic profile by the variation of light/darkness cycles. Objectives: To determine the effect of light/darkness variation on lipid profile of Rattus norvegicus. Methods: 20 rats (Rattus norvegicus) was used separated in two groups (control and experimental) and housed with variances in light/darkness cycles. Thereafter a blood sample was taken in order to dosage lipid profile (cholesterol, triglycerides, HDL and LDL) before and after variation of light/darkness cycles. Statistical analyses were conducted using Student’s t-test for cholesterol, triglycerides, HDL and LDL Results: Normality of ...