Enzymes are molecules that are necessary for life and by structure they are mainly proteins. They catalyze reactions in a way that they stabilize transitional state and can speed up the reaction by a factor that can be bigger than a million. The deficiency of only one enzyme can be fatal for the body. They are highly specific for the reactants (substrates) of the reactions that they catalyze. Inhibitors are the molecules that reduce the activity of an enzyme and many reversible inhibitors are also effective drugs. Alzheimers disease is a progressive degenerative disease of the central nervous system. It is one of the most common type of dementia with a frequency of 5 % diseased from the age of 50 and over and 50 % diseased of people over the age of 80. Acetylcholine is a transducer of nerve impulses that regulates memory and processes of learning and it maintains the level of consciousness. Acetylcholinesterase is an enyzme that catalyzes the hydrolysis of acetylcholine by interrupting the transmission of a nervous pulse. Various acetylcholine inhibitors are good drugs for Alzheimer disease. According to the cholinergic theory, in Alzheimers disease the cholinergic neurons are dying away and the synthesis of acetylcholine is reduced. The inhibitors are slowing down the hydrolysis of acetylcholine and there by increasing its concentratition, enabling normal functioning of the brain. In this thesis, the inhibition effectiveness of alkaloid huperzine A and monoterpene β-pinene on acetylcholinesterase activity, were tested. According to the experimental data it can be concluded that they are both good acetylcholinesterase inhibitors and that they could be used in the treatment of Alzheimers disease.