Turmeric (Curcuma longa L.) belongs to the Zingiberaceae family, widely grown in warm, rainy regions such as India, Indonesia, Malaysia, and South China, with traditional uses against biliary disorders, anorexia, coryza, cough, diabetic wounds, hepatic disorder, rheumatism, and sinusitis, and diarylheptanoids as principal active constituents. Chromatographic separation of its rhizome extract gave four compounds. Compound 1 was identified as 1-dehydrogingerdione via 1H NMR, which is the first report of isolation from Curcuma longa, and its origin from the plant was confirmed by excluding adulteration or contamination. GC/MS analysis of turmeric oil identified ar-turmerone, (–)-caryophyllene oxide, and β-turmerone. The CHCl3 fraction afforded three major curcuminoids (curcumin, demethoxycurcumin, and bisdemethoxycurcumin) purified by TLC. The phytochemical investigation led to the isolation and identification of several known natural products, including 1-dehydrogingerdione reported for the first time from Curcuma longa.