Reproduction success rate of Cattle Egret Bubulcus ibis Linnaeus, 1758 carried out on the island of Ali Siah in Karon River in Ahvaz city since January 2013 and was completed in May 2014. In this study, the stages and success rate of species was measured in 60 nests. Observations showed that the start of nesting was late in December, the mean hatching time of eggs were 22 days, the average number of eggs per nest was 3.9, the average growth time of the chickens was 33 days, the end of the breeding was early in June. Measuring the size of 234 eggs in 60 nests showed that the average egg shape index was 75.56, the average volume of eggs was 20.99 ± 14.8 cubic meters, the mean small diameter of the eggs was 28.36 ± 1.96, the mean large diameter of the eggs were 37.73 ± 1.26 mm, the mean weight of eggs were 24.41 ± 4.34 gr, and the mean weight of nests were 463.98 ± 9.40 grams. The average Nestling time was 13 days, the average Post-Nestling time was 16 days, and the average total flight time for chickens was 14 days. The breeding period was 84-90 days and the reproductive success rate was 73.33%. The breeding population of Cattle Egret on the Ali Siah Island was estimated 448 pairs. Observations in 2015 showed that the Ali Siah Island was destroyed and breeding colony of the Cattle Egret was destroyed on this island.