Reaction of NH(a 1Δ) with methanol has been studied by a flash photolysis of HNCO at 193 nm at room temperature (298 ± 2 K). Time dependence and relative concentrations for NH, NH2, NHD, CH 3O, H, and D are monitored by a laser induced fluorescence (LIF) technique. From the pseudo-first-order analysis of NH(a 1Δ) decay rate, the rate constants for the reactions NH(a 1Δ) + CH3OH→ products (1), and NH(a 1Δ) + CH 3OD→products (2) have been determined to be k1 = (1.37 ± 0.10) X 10-10 cm3 molecule-1 s-1 in the pressure range of 3-20 Torr Ar or 5 Torr He, and k 2=( 1.33 ± 0.05) X 10-10 cm3 molecule-1 s-1 at the pressure of 5 Torr He, respectively. By comparing the LIF intensity of NH(X 3Σ-) in reaction (1) with that in NH(a 1Δ) + Xe reaction system, the contribution of physical quenching in reaction (1) has been evaluated to be less than 2.4%. Also by comparing the LIF intensities of NHD and NH2 in reaction (2) with those in NH(a 1Δ) + D2/H 2 reaction systems, the branching ratio between the pathways producing NHD (2b) and NH2 (2c) has been determined to be k (26)/k(2c)=23 ±9. It is elucidated that the insertion of NH(a 1Δ) into O-D bond of CH3OD is completely predominant over C-H bond; i.e., the O-D bond is about 69 times more reactive toward insertion of NH(a 1Δ) than a single C-H bond.