The attack took place on a beach near Recife in the tourist-rich state of Pernambuco on Thursday. The boy was taken to hospital but did not survive, the state government's shark monitoring committee said.
There were four signs warning of sharks on the beach in question, and on many other beaches in Pernambuco, but security will now be increased.
Over 80 shark attacks have occurred in Pernambuco since 1992, 27 of them fatal.
