The life cycle of poplar leaf beetle, Chrysomela populi L. which attack poplar studied in Iraq during season 2013.The study showed the mean of incubation period, hatching percent and larval stage (5.61 day, 87% and 8.1± 0.80 day) respectively. It was appeared that the larval stage lives and feed on the poplar leaves. The pupal instar was 4.8 days. After the emerge of adult it laid the eggs on the lower surface of the leaves with groups. The study also indicated that the mean number of eggs laid by a single female were 105.3 egg. The sex ratio of male to female was 1:1.7. The longevity of adult, males and females were 47.10 ,56.21 days respectively. Also it was found that this beetle has two generations per year. The hibernation appeared in the adult stage. Ecological study has shown that the area and percentage of damage started with the primary appearance of the poplar leaves beetle adults as the beginning of April .The increasing of insects number caused an increase in the area and percentage of damage which reached their maximum means 10.70,16,30 cm2 and 12.10 cm2 , 41.18 , 45, 00 and 17.3% for Populus euphratica , Populus nigra and Populus deltoids respectively , this happened when the insects number means reached the maximum 2.00 ,2.75 and 2.30 insect / leaf for the above mentioned poplar species at mean temperature 27.30 C 0 and R.H. 32.5 % . The statistical analysis showed that there is a significant correlation between the mean insect number and mean of area and percentage damage of the three poplar species with r value (93.45, 90.16 and 89.25) for damaged area and for damage percentage (90.86, 88,71 and 89,60) respectively.