Antioxidant, anticholinesterase and antidiabetic activities of three curcuminoids isolated from the Curcuma longa were simultaneously tested and compared in this study. The highest antioxidant power was detected for curcumin with the applied methods. The drug potentials of curcuminoids for Alzheimer's disease were controlled. Bisdemethoxycurcumin (BDMC) showed substantial inhibitory activity. The activity of demethoxycurcumin (DMC) followed BDMC, whereas curcumin showed very little acetylcholinesterase inhibition activity. Antidiabetic activity of curcuminoids was evaluated by their -glucosidase inhibitory activities. All curcuminoids show activities with decreasing order as BDMC>curcumin>DMC. The significant activities of BDMC compared to its isomers and examination of chemical structures of isomers might be a starting point in designing new drugs for Alzheimer's and Diabetes Mellitus.