Abstract: The study was conducted to calculate field infestation rate by using the infestation rates of blind bolls of Pink Bollworm, PBW (Pectinophora gossypiella Saund.) and Spiny Bollworm, SBW (Earias insulana Boisd.) in Harran Plain in 2002-2003. At the end of the study, the population of SBW and PBW were found in large areas of Harran Plain and the significant yield reduction was recorded and the infestation ratio of the pests had shown a higher ratio in 2002 (61.02%) than that of in 2003 (58.55%). The average infestation ratio of both years was 59.78%. While the number of PBW`s larvae were 6258 and 5935 in the examined 4500 bolls per year in 2002-2003, SBW`s larvae were 82 and 68, respectively. A parallelism was detected between the infestation ratio and the number of larvae of these pests. It can be understood from the number of larvae, PBW larvae had a higher infestation ratio than that of SBW in collected bolls. While the highest number of PBW larvae found in a blind boll in 2002-2003 was 4.01±0.25 and 4.86±0.22, the minimum of PBW larvae was 1.00±0.57 and 1.10±0.33, respectively. Field infestation ratios were found as 13.79 and 15.40% in 2002 and 2003, respectively.