•High-resolution laser spectroscopy of the B–X transition of nitrate radical.•Rotational assignment based on the ground state combination differences.•Zeeman effect of rotational lines.Rotational assignment of the high-resolution fluorescence excitation spectrum of the 14NO3 radical in the B∼2E′ ← X∼2A2′ transition 0–0 band region located around 15,100 cm−1 was made with the help of the ground state combination differences and the observation of Zeeman effect. We successfully identified several rotational line series based on the newly obtained rotational assignments of 162 lines with |k″| ⩽ 15 and J′ ⩽ 18.5 quantum numbers, and we estimated the effective molecular constants of the excited vibronic states.