To assess the effect of Nigella sativa (N.S) oil supplements on CVD risk factors in a crossover design for the first time. Methods Obese and overweight healthy women were randomized to receive N.S oil (2000 mg/day) and placebo. This intervention period lasted for 8 weeks and separated by a 4-week washout period. An iso- caloric diet was given to every individual throughout the study. Blood pressure, lipid profile, atherogenic indices and liver enzymes were measured. Pkcross procedure was performed for statistical analyses using Stata software. Cohen's d was estimated as effect size for all outcomes to measure the magnitude of the effects. Results Thirty-nine participants completed the study. Capsules of N.S increased serum highdensity lipoprotein cholesterol (Cohen's d : 0.47, P : 0.009), reduced lowdensity lipoprotein cholesterol (Cohen's d = _ 0.33, P = 0.031), reduced TC,' HDL-C ratio (as an atherogenic index, Cohen's d = 0.9, P