Determining of some morphological and biological characteristics of Palomena prasina L. (Heteroptera: Pentatomidae) This study is a part of comprehensive research on Palomena prasina L. (Heteroptera. Pentatomidae) (Green shield bug) that was carried out in Samsun province between 20032004 years. The study was conducted in laboratory (25±2 °C and 55-65 % R.H) and field conditions. In laboratory; development time and ratio of egg and nymph stages were determined. Body length and prothorax width of each nymphal stages and adults were examined for Dyar and Prizbam rules. Colour preference of adults with using 9 colour was determined by free-choice test. By the field experiments; adult longevity in cages, colour changing during the seasons, mating, sex ratio and sexual differantiation were studied. Data from five nymphal and adult stages did not fit to Dyar and Przibam rules. The correlation was very important between prothorax width and body length in all nymphal and adult stages. Eggs hatching ratio was 96.4 % and hatching time was 8.02 days. Total nymphal stages were 51.2 days as average and development ratio of nymphs to adult stage was 28 % on bean seeds. The adults showed significant attraction to yellow colour in free-choice test. In field conditions, two main colours, green and brown, were observed in adult stage and brown adults occured after end of July. Both colours were seen in equal in population and there was no difference in coincidence. Overwintered adults had dark green colour in