When a Zn wire was heated by electric current, ZnO whiskers grew on the wire surface. The average diameters of the whiskers grown under O 2 , 20% O 2 and Ar atmospheres were 0.12, 0.17 and 0.4 μm, respectively. The well-known visible emission was observed from the whiskers grown under O 2 and 20% O 2 atmospheres. The whiskers grown under Ar atmosphere showed strong ultraviolet (UV) emission. X-ray diffraction measurements revealed that the crystalline quality of the whiskers increased with decreasing O 2 concentration in the growth atmosphere. It was found that residual O 2 of less than 10 ppm in Ar atmosphere is used for the synthesis of the whiskers with UV emission. Monitoring O 2 concentration during the electric current heating of Zn wire in Ar atmosphere was effective in estimating the yields of the whiskers.