The hostages were Nigerian employees of Chinese oil servicing firm Sinopec, navy spokesman Commodore Kabir Aliyu said.
They were kidnapped by a gang called the Lapto Marine Force operating around the Bakassi waterways in Cross Rivers state and freed in the naval operation late, he said.
"The gang ... has been terrorizing people around Bakassi waterways, killing, robbing, as well as engaging in piracy and abduction," he added.
Piracy and kidnapping are common around the Niger Delta. West Africa's oil-rich Gulf of Guinea is second only to the waters off Somalia for the risk of attacks.
Four foreigners working for Netherlands-based Sea Trucks Group who were kidnapped by pirates off the Nigerian coast on August 4 were released last week.