To provide a silicon nitride sintered compact and a heat conduction member having high heat conductivity and corrosion resistance to alkali components. A silicon nitride sintered compact having a silicon nitride crystal and a grain boundary phase including an oxide of sodium and/or an oxide of potassium, wherein the content of the oxide of sodium and the oxide of potassium is 0.2 mass% to 1 mass% inclusive of the entire mass in terms of the total of the values converted to Na2O and K2O, respectively. High heat conductivity and high corrosion resistance to alkali can both be provided by satisfying this configuration.