The terrapins of the northern part of Iran belonging to the family Emydidae have two species named European pond turtle, Emys orbicularis and Caspian pond turtle, Mauremys caspica caspica .In this study, 89 specimens were collected between 1999-2001 from 22 sampling stations in Golestan and Mazandaran provinces, were biologically studied in terms of their morphology, morphometery, feeding, reproduction, behaviour, karyology and parasitology. Most of samples were captured in hot days of spring and summer. Male and female are distinguishable specially on the basis of iris color that is red in male and yellow in female. They arc carnivorous and lay almost 7 eggs every year. Males are ruder than females. The somatic chromosome numbers were determined 2n = 26. Turtle leech, Haementeria costata belonging to the order Rhyncobdellida was identified in some samples. Statistical results show that %91 of males and females are different in measured traits. Comparison between TL1 (base of tail length) and TL2 (tail length) shows that I anus position is different in males and females. In this study, sexual ratio (Male/ Female) is 1/4.5.