This work aimed to study the relationship between phases of lunar lighting and population peaks of American bollworm (ABW), Helicoverpa armigera (Hub.)  moth. It was carried out at Zefta district, in Gharbia Governorate, Egypt during four successive cotton seasons (2005-2008), Results showed that of H. armigera moths population had five to six peaks per season. At Gregorian months, moth peaks occurred at different dates per month, during the four seasons. Whereas, at lunar months, they occurred at constant moon phases (at the new moon or at the first quarter every month) in the same seasons. The scoto phase period (new moon) had a positive effect on the activity of moth populations, while, a negative effect was during the highest luminosity (full moon). The relationships between the percentages of moon light and moth populations were, in general, negative and highly significant and led to a linear regression equation. This information, cold aid the decision makers to better except the timing of the  highest moth populations that produces different stages of this pest and  reduces / eliminate their damage to cotton plants using available control methods.