Herbal plants are a reservoir of potential phytochemical compounds and the richest bioresource of drugs for traditional systems of medicine, nutraceuticals, food supplements, modern medicines, pharmaceutical intermediates, folk medicines, and chemical entities for synthetic drugs. In the present study we find out phytoconstituents of Nigella sativa and quantitative densitometric analysis of its bioactive compound thymoquinone in the different solvent extracts. It was found that Nigella sativa seeds were extracted with ethanol, methanol, and benzene as solvents. Phytochemical analysis showed the presence of potent bioactive constituents such as alkaloids, phenols, tannins, trepenoid, saponins, and steroids in methanol extract. Benzene extracts have only alkaloids and steroids. While ethanol extract showed the presence of alkaloids, phenols, tannins, proteins, amino acids, flavonoids, terpenoids, saponins, and steroids. The high-performance thin layer chromatographic method (HPTLC) was employed to quantify and densitometrically analyze thymoquinone in methanol, ethanol, and benzene extract of Nigella sativa. The analysis was performed on an aluminum plate with a mobile phase of n-hexane: ethyl acetate: methanol (7:2:1 v/v/v) and a densitometric measurement using a TLC scanner (CAMAG) at 254 nm. The ethanol extract of N. Sativa exhibited single sharp peak of thymoquinone with 0.85 Rf value, the highest area of the band 8137.6, and a total recovery of was 98.08% which is nearly equal to the standard thymoquinone with Rf value (0.85), the highest area of the band 8789.4 and total recovery was obtained 100%. The present research indicated that purified thymoquinone from N. sativa is a potential source for therapeutic application. Keywords: Phytoconstituents, Herbal extract, Essential oil, Quantification, Chromatography.