The aircraft, acquired from the US, were inducted during a ceremony held at the Pakistan Navy base Mehran in Karachi.
The aircraft are part of a batch of seven P-3C Orion aircraft Pakistan will get from the US.
The next set of the aircraft would be arriving in the later part of this year, the Navy Chief said.
US defence major Lockheed Martin upgraded the aircraft by equipping them modern avionics and other systems.
The P3C Orion has been designed for carrying out reconnaissance, anti-ship and anti-submarine surveillance warfare missions.