The pirate had kidnapped the six sailors, also including Ukrainians and Russians, after storming oil service ship Armada Tuah in southern Nigeria and demanded a ransom of $1.3 million, officials said.
Last month, five Indians kidnapped in a similar manner in December were released but no mention was made of any ransom payment.
Piracy is common in Nigeria especially in the oil-rich Delta region. Attackers would go for oil-laden cargo or kidnap ship crews for ransom.
Nigeria is Africa's top oil producer.