Dalmatian chrysanthemum belongs to the family of Asteraceae. The plant inhabits dry and rocky areas and it is a strictly protected species. The plant, other than having pharmacological, antioxidative and inhibitory activity also possesses insecticidal properties. Pyrethrins found in the seeds of the plant have a toxic effect on the nervous system of insects, fish and snakes, while the toxicity is far less effective with mammals and birds. Acetylcholinesterase (E.C.3.1.1.7.) is a serine esterase that breaks down the neurotransmitter acetylcholine to acetate and choline. Inhibition of this enzyme plays a key role in alleviating the symptoms of Alzheimer's dementia. Alzheimer's dementia is a severe incurable illness that, with its progress, leads to loss of memory, inability to think and conduct daily activities. The aim of this paper was to examine the chemical composition and the anticholinesterase activity of essesntial oils of the plant isolated from the head of the plant during different flowering times in the natural population of the plant on the island of Brac. GC/ MS instrumental technique was used to determine the chemical composition and the amount of terpene and non-terpene active substances present and for testing the inhibition of the enzyme AchE Ellman's method was used. The most common components of the oil are non-oxidized sesquiterpene compounds β-himachalene, β-guaiene, β-selenine, γ-himachalene and δ-selenine. Chrysanthemic acid, the acid whose esters participate in the formation of the pyrethins, is identified only as an ingredient of the oil isolated from the flowers of the plant harvested in the lastest flowering time. Isolated essential oils do not have the ability to inhibit the acetylcholinesterase