•Ce addition suppresses the phase decomposition of 2:14:1 main phase due to La doping.•La substitution make grain refining of NdFeB based alloys.•Magnetic properties of La-Ce co-doped alloys are superior to single-doped alloys.•The (BH)max of Nd0.5(La0.6Ce0.4)0.52Fe14B reaches 12.4MGOe.•La-Ce co-doped NdFeB alloys can be applied due to its ideal magnetic performance. Investigation of the phase structure of Nd1−x(LayCe1−y)x2Fe14B (x = 0–0.7, y = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) melt spun ribbons and their magnetic properties is presented. The La-Ce co-doped Nd-Fe-B alloys are compared with the La doping and Ce doping respectively by controlling the doping ratio of La/Ce. It can be found that the Nd-Fe-B alloys remain single 2:14:1 phase with Ce doping. In contrast, the 2:14:1 phase begins to decompose when the doping content of La reaches 30at.%. The 2:14:1 phase decomposes seriously with the La doping content over 50at.%, accompanied by the rising of secondary phases. The magnetic properties of Nd-Fe-B alloy decrease with the increasing of La, Ce doping content. The performance of La-doped Nd-Fe-B is superior to that of Ce-doped when the addition of La is less than 50at.%. However, severe phase decomposition of 2:14:1 phase with x more than 0.5 leads to the sharp decline of magnetic properties of La-doped Nd-Fe-B. In general, the magnetic properties, especially for the Br and (BH)max of La-Ce co-doped Nd-Fe-B are better than single-doped cases. And the co-doped Nd-Fe-B alloys show greater enhancement of (BH)max with the increasing amount of total doping content. For example, when the total doping concentration reaches 50at.%, the (BH)max of Nd0.5(La0.6Ce0.4)0.52Fe14B still reaches 12.4MGOe, which is much higher than (Nd0.5Ce0.5)2Fe14B ((BH)max = 8.2MGOe).