The present Ph.D thesis describes the phytochemical and biological exploration of two species belong to family Ranunculaceae of District Dir (U), Khyber Pakhtunkhwa Pakistan. The main goal of our research was the isolation, structure elucidation, selective AChE and BChE enzyme inhibition of C19 and C20 diterpene alkaloids from the basic chloroform soluble fraction of D. chitralense and D. denudatum Wall. Seven new compounds; Chitralinine-A (1), Chitralinine-B (2), Chitralinine-C (3), Chitraline-A (4), Chitraline-B (5), Chitraline-C (6), Chitraline-D (7) and two known, Ajaconine (10) and Delectinine (11) have been isolated from the aerial part of D. chitralense. Two new Jadwarine-A (8) and Jadwarine-B (9) and one known dihydropentagynine (12) have been isolated for the first time from the aerial parts of D. denudatum Wall. All the isolated compounds (1-12) were characterized by various spectroscopic techniques and screened for enzyme inhibition activities (AChE & BChE). The isolated compounds were found to be potent AChE and BChE inhibitors. Our present findings indicate the interest of C19 and C20 diterpenoids as potent AChE and BChE inhibitors present in the investigated two delphinium species. They may contribute towards naturally accessible inhibitors used for the treatment of Alzheimer’s disease.