The ability to distinguish gender among insects is essential to their study and management. The objective of this work was to find sexual dimorphism between males and females of Oncideres ocularis Thomson, 1868 based on their external morphology. Twenty-seven morphometric variables from the body of males and females of this beetle were measured. The length of body, elytra, length and width of the head, and length of antennae were found to have different dimensions between genders. The antennae in males can be two times longer than the elytra, while in females it is one and a half times longer. The length of the last antennal segment of males is almost seven times longer than the pedicel, while in females the difference is only about two and a half times longer. Males and females of O. ocularis can be separated based on the length of the last antennal segment.