Aims: Evaluate the insecticidal effect of the aqueous extract of neem leaves on the control of Costalimaita ferruginea in eucalyptus. Place and Duration of Study: Entomology Laboratory of the Center for Agricultural Sciences (CCA) of the State University of the Tocantina Region of Maranhão (UEMASUL) between November 2016 and July 2017. Methodology: Neem aqueous extract solutions were tested at concentrations of 40, 60 and 80%, and the control group treated with mineral water. Leaves of eucalyptus seedlings were immersed in each concentration and individualized in Petri dishes together with the insects. The design was completely randomized with four treatments and ten repetitions, each repetition consisting of a Petri dish with an insect and a eucalyptus leaf. The evaluations were carried out daily, analyzing the mortality of adults, and the leaves were replaced by others submitted to the same treatment and procedure described above. Results: In the evaluations of 12, 60, 72 and 84 hours there was no significant difference. 36 hours after the implementation of the experiment, the 60% neem concentration resulted in 100% mortality of specimens. Conclusion: The 60% neem concentration is the most efficient due to its rapid effect on C. ferruginea mortality and economy of raw material for production.