Possibility of a real-time tritium monitoring in high-energy accelerator facilities is examined using a polyimide hollow-filament type membrane module. Enrichment characteristics of hydrogen isotopes in nitrogen and water in dry-air were measured extensively, and a computer simulation using the simplified model for the gas separation was also performed. The experimental results showed that the polyimide membrane module could enrich significantly hydrogen isotopes and water vapor from nitrogen and dry air. It is concluded from these experimental results that using the membrane module could be useful for the real-time tritium monitoring.