Venezuelan officials say six prisoners died and more than a dozen were injured after fighting broke out between rival gangs in a jail in Yaracuy state.
The clashes at the San Felipe prison, some 500km (310 miles) west of Caracas, followed the murder of one of the gang leaders, officials said.
Violence also erupted at a jail in Cabimas, in Zulia state, where one inmate died in a fire.
Venezuelan prisons are seriously overcrowded and see frequent riots.
Last week, a stand-off ended at a jail in Guatire after nearly a month when armed prisoners surrendered.
More than 25 people had died in clashes and in subsequent attempts to regain full control of the prison.