An amphoteric compound 4-hydroxyaminoquinoline 1-oxide(4-HAQO) was oxidized by oxygen to lose one electron from NHOH group of the molecule and to produce a stable free radical. This oxidative radical production was accelerated by addition of several kinds of oxidants. The UV-absorption of the free radical thus produced, showed its maximum at 455mμ. On the other hand, the oxidation of 4-HAQO was protected by the presence of such a reducing agent as ascorbic acid. As a result, the presence of such a reducing agent made it possible to record the UV spectrum of 4-HAQO in alkaline media.