All four were found dead in the basement of the house where they were manufacturing illicit liquor.
The incident took place in Rajpur Kesariya village under Dilari police station in Moradabad.
Rajendra Singh, his two sons and one labour were found dead in a small room made in the basement of his house.
The police reached the spot after the information of the incident and sent the bodies for post mortem.
Preliminary investigations have revealed that Rajendra Singh used to make and sell illicit liquor. Even a year ago, 250 boxes of illicit liquor were recovered from his house, after which he was sent to jail.
After coming out from jail, Rajendra Singh again started making illegal liquor with his two sons.
Rajendra Singh’s wife Phoolwati first saw the four lying unconscious and informed the neighbours.
The neighbours informed the police but by the time the police arrived, all four had died.
Moradabad SSP Pawan Kumar said that a forensic team had also been called to the spot and further investigations were underway.
The bodies have been sent for post mortem.