Abstract: Since the 1980s, China Institute of Atomic Energy has designed and built nine miniature neutron source reactors (MNSR) at home and abroad, which has high enrichment uranium (HEU) as fuel. With the international situation of nuclear non-proliferation, the conversion of MNSR from HEU to low enrichment uranium (LEU) is highly concerned by the international community. While the MNSR power and core size are unchanged, physical calculation, structural design, safety analysis and experimental measurement were carried out for LEU core design, HEU unloading, LEU loading and experimental technology. UO₂ with ²³⁵U enrichment of 12.5% was used to replace U-Al with ²³⁵U enrichment of 90% in prototype MNSR LEU conversion. MNSR with the LEU core can meet the application requirements, and it still has good inherent safety characteristics.