The incident came to light last night when locals complained of foul odour emanating from the flat following which police reached the spot and recovered all the bodies in a highly decomposed state after breaking the doors open.
According to preliminary reports, the four - Ranjit Yeshwantrao (45), his wife Swati (38) and two daughters Shraddha (14) and Arya (7)- died between January 26 and January 31.
While three of them were lying dead on the floor, Ranjit's body was found hanging from the ceiling fan, police said.
Also, he is said to have taken the extreme step due to financial distress, police said.
An offence under Section 302 of IPC has been registered and the bodies have been sent for postmortem.
Police also said that before the incident, the family had misled their relatives saying they will be out of town for a while since they were going on a pilgrimage.