Using 462 fb(-1) of e(+)e(-) annihilation data recorded by the Belle detector, we report the first observation of the decay D-s1(2536)(+)-> D+pi K--(+). The ratio of branching fractions B(D-s1(2536)(+)-> D+pi K--(+))/B(D-s1(2536)(+)-> D*K-+(0)) is measure