Boiling heat transfer and flow characteristics were investigated in vertical upward flow of liquid nitrogen. Observed boiling heat transfer was in a nucleate boiling mode. Heat transfer coefficients in the nucleate boiling mode were well correlated by Schrock-Grossman's equation. Flow patterns observed in this experiment were classified mainly into single-phase flow of liquid, bubbly flow, slug flow, annular flow and inverted annular flow. Based on the experimental observation, the flow regime map for LN₂ was presented, and the applicability of the flow-regime transition criteria by Mishima-Ishii was verified.