Overwinter biology of Orius niger (Wolff, 1811) (Hemiptera: Anthocoridae) was studied during 2014 and 2015, in Adana Province, Turkey. Outdoor experiments were performed at the Department of Plant Protection, Faculty of Agriculture, University of Cukurova on seven different dates between October and April. The predatory bug, O. niger, overwinters in Adana Province as adults. Some biological parameters of the O. niger were investigated under outdoor conditions at monthly intervals from autumn to spring with cotton seedlings placed in vials with distilled water. Sterilized eggs of the Mediterranean flour moth, Ephestia kuehniella Zeller, 1879 (Lepidoptera: Pyralidae), were provided to Orius as food. All eggs of O. niger hatched even at the low temperatures in winter. Most of the experimental females laid eggs. Total mean numbers of eggs laid by the females was the highest in April (83.55 +/- 15.60 eggs/female) and the lowest in December (7.71 +/- 1.62 eggs/female). Duration of oviposition of the experimental females was nearly 30 days in October, November and April, but less than 30 days in other winter months. The proportion of non-reproductive females in December-February ranged from 25% to 40%. Longevity of females was nearly a month in winter and they did not survive until spring. While sex ratios (male/female) ranged from 1: 2.5 to 1: 3 in October-January, the ratio was 1: 1 in April. Duration of nymph development was the highest (45 days) in January and the shortest (nearly 18 days) in April. Furthermore, most of the first instars of nymphs died in a short time due to cold winter days in December-February, and nearly 28% total nymphs matured to adults. The experimental results support that O. niger can severely decrease the population sizes of pest species in late spring (after April) in countries of the southern zone.