Feyzullayev Nijat Aga-Zaki oglu was born on January 22, 1932 in Baku. He studied at the Biology Faculty of the Azerbaijan State University (1950-1955).
N.A.Feyzullayev defended his dissertation on philosophy (1962) and doctor of sciences (1983) and was awarded the title of professor (1996). He was elected a corresponding member of the Academy of Sciences of Azerbaijan (2001).
In 1956 he began his career at the Institute of Zoology of ANAS, first as a laboratory assistant (1956-1964), then as a senior research assistant (1964-1974), and from 1974 until the end of his life as head of the Laboratory of Helminth Systematics and Biology (1974 -2001).
He was one of the researchers of the parasites of birds, fish and mollusks in Azerbaijan. He participated in the Ecological and Faunistic Study of Birds of Black and Caspian Seas in the Soviet-Bulgarian Studies.
N.Feyzullayev studied some nematode groups and other parasitic organisms and gave a new parasitological concept - "mesoparasite" and explained its genesis. He has identified the factors that cause resuscitation in trematodes during adaptation. He discovered the migration of the Cycloceloidea metasercarcin in the body of the latter, revealing the causes of inter-species antagonism in the joint nutrition of parthenite trematodes.
N.Fayzullayev is the author and co-author of 140 scientific works. 52 of them were published abroad.
He is the co-author of 5 monographs published in Baku, Tbilisi and Moscow. He was one of the authors of the third volume of the "Wildlife of Azerbaijan". Under the guidance of the scientist, 10 doctoral dissertations were defended.
He was awarded honorary medals of the Academy of Sciences of the USSR "Academician Y.N.Pavlovski" and "Academician K.I.Skryabin".
Corresponding member of ANAS Fajzullaev Nijat Aga-Zaki died on July 20, 2001.