Chalcosoma engganensis is a large (35–60 mm) and heavy beetle.

The male has a sharp horn (directed obliquely upward and forward) on the head.

On each side of pronotum there are curved, forward directed horns.

This species differs from the normally developed specimens of the other Chalcosoma species in that horns are shorter, male can look a lot like small copies of Chalcosoma moellenkampi.

The female lacks these horns and spikes, and is smaller.