A time-resolved quasi-elastic laser-scattering (QELS) technique was applied to monitor the molecular number density at a water/nitrobenzene (W/NB) interface of a W-NB-W three phase chemical oscillation system. We successfully monitored the oscillations of interfacial molecular number density, electric potential, and turbidity simultaneously by a newly developed chemical oscillation - QELS combination system. We observed for the first time that monolayer of the surfactants covers the interface almost throughout the oscillation and that the oscillation occurs simultaneously with a catastrophic disintegration of the monolayer after the increase of molecular number density. We proposed a new model for the chemical oscillation based on the obtained molecular description. (C) 1998 Elsevier Science Ltd. All rights reserved.