The game was evenly poised during the first 35 minutes as both teams played an attractive, attacking brand of football.
The Kolkata-based club took the lead in the 36th minute through S K Jewel Raja, who tapped in a cross from the right flank.
Although there were no further goals in the first half, Mohun Bagan forwards made several attempts to increase the lead.
In the second half, Toljay Ozbey slipped the ball past J&K custodian Vikramjeet Singh in the 54th minute while captain Odafa Onteka Okalie made the scoreline read 3-0 with a strike in the 63rd minute.
Manish Nathani completed a miserable evening for the J&K team by scoring for the visitors in the 68th minute.
This was the third friendly game between a Kolkata-based football outfit and Jammu and Kashmir state team.
Mohammaden Sporting played two friendlies in the valley with hosts emerging as the winners in both the games.