At closing time, the head of a black 'Diceros bicornis' rhinoceros exhibited in the mammals gallery was stolen by three people," the museum said in a statement issued after the Tuesday heist.
The rhino robbers fled to a waiting car with a driver, with museum guards in hot pursuit. "They got away before we could catch then," the museum added.
Located a stone's throw from the European parliament in central Brussels, the museum is popular for its celebrated dinosaur skeletons and on Wednesday stepped up security while taking rare prized pieces away from the public eye.
On June 16, a robber also working with an accomplice stole a rhino head in the Liege natural history museum but was caught and the head returned to its place.
The man made off to a waiting vehicle with Dutch number-plates after tear-gassing the guards but police threw up roadblocks and brought in the pair, both Poles.