The prisoner, Liladhar Bordoloi, was found hanging from the hook of the fan in his cell by jail employees this morning, Morigaon Additional Superintendent of Police R K Handique said.
Bordoloi had hanged himself with a rope made from his clothes, he said.
Bordoloi was sentenced to life imprisonment last year for stabbing his wife, Rita Bordoloi, to death in July, 2014.
His body has been sent for post mortem and further investigations were on, Handique added.