At stumps on the second day's play, Jharkhand were 196 for four in reply to Assam's first-innings total of 191 all out at the Nehru Stadium.
With six wickets remaining, the visitors would look to consolidate their lead tomorrow.
Wicketkeeper-batsman Ishan Kishan top-scored for Jharkhand with 126-ball 60, and struck nine fours during his stay in the middle.
Assam had resumed at their overnight score of 133/6. Arun Karthik top-scored for the hosts with a 165-ball 97. He hit 13 fours.
Brief scores:
Jharkhand 1st innings: 196/4 in 69 overs (Ishan Kishan 60).