Bulk amorphous Ni_(57)Ti_(18) Zr_(20)Si₃Sn₂ feedstock was sprayed using a high velocity oxy-fuel spraying process. In order to evaluate the amorphous formability ign view of chemical instability, the oxygen to hydrogen gas flow rate ratio was changed at the constant total gas flow rate. Flame gas enthalpy was increased with the O₂/H₂ gas ratio. In-flight particle melting state was improved with the increase of oxidizer flow rate. Fthe amorphous phase fraction within an as-sprayed coating was decreased with the oxygen flow rate. From the thermal analysis and x-ray diffraction, the effects of 0₂/H₂ gas ratio on the crystallization of HVOF sprayed bulk amorphous Ni_(57)Ti_(18) Zr_(20)Si₃ could be divided into two categories. One is due to the solid-state crystallization during flight along the low gas enthalpy The other results from the of bulk amorphous feedstock due to the chemical composition change resulting from in-flight particle oxidation at the higher oxygen gas flow rate.