Cotton-seed-bug (CSB), Oxycarenus hyalinipennis (Costa) is a serious pest of cotton and other malvaceous, the present investigation aims to determine some biological features, developmental threshold and thermal requirements (degree-days, DD's) for cotton seed-bug, Oxycarenus hyalinipennisin Egypt. Effect of three constant temperatures (25, 30 and 35±1°C) on developmental rates of different stages of cotton-seed-bug was detected. The incubation period, nymphal and adult durations, pre-oviposition, oviposition and post-oviposition periods, male and female longevities, sex-ratio, fecundity, fertility and generation time were estimated. Data obtained revealed that, time required for development of all stages were decreased as temperature increased. Egg incubation periods were 6.66±0.36, 5.66±0.33 and 4.33±0.66 at 25, 30 and 35°C respectively. The highest percentage of egg-hatching was 98% at 25°C, and the lowest was 88% at 35°C. The nymphal durations were 25.2±0.17, 17.11±0.27 and 13.88±1.17 days at 25, 30 and 35°C. The lowest adult longevity was 19.87±1.67 day at 35°C and the highest was 37.48 days at 25°C. The sex-ratio between males and females was nearly 1:1 at both temperatures 25 and 30°C, while it was 2:1 at 35°C. The highest female fecundity was 227.7 eggs at 25°C and the lowest one was 83 eggs at 35°C. The same trend was reported for female fertility. The lower developmental threshold for egg and nymphal stage and adult longevity were 7, 12.51, and 13.85 °C, respectively and the corresponding thermal requirements were 123.8, 285.36 and 421.36 DD's.