We report a crystalline compound 2-azido-4,6-dimethoxy-1,3,5-triazine (ADT) as an intrinsically safe, highly efficient, and shelf-stable diazo-transfer reagent. Because the decomposition of ADT is an endothermal process (Δ H = 30.3 kJ mol-1), ADT is intrinsically nonexplosive, as proved by thermal, friction, and impact tests. The diazo-transfer reaction based on ADT gives diazo compounds in excellent yields within several minutes at room temperature. ADT is very stable upon >1 year storage under air at room temperature.