An environmentallyfriendlymethod was established for the N‐methylation of the 5‐substituted 1H‐tetrazoles with a greenreagent: DMC. DABCO was the optimal catalyst, and hazardous chemicals were avoided in this protocol. A plausible catalytic mechanism is proposed, which consists of a DABCO‐activated process and a thermally induced rearrangement of tetrazole carbamates.