Absorption of sulfur dioxide in N-formylmorpholine results in the reversible formation of 1:1 complex, as shown previously. This paper presents a kinetic investigation of the liquid-phase reaction. This reaction was assumed to be a fast process and this work was aimed at the verification of this hypothesis. Absorption of sulfur dioxide either as pure gas or diluted into an inert, was carried out at 25degreesC in a stirred vessel with a flat interface. The experimental data were modelled under the assumption of a fast reversible formation of a SO2-NFM complex. The comparison between experiment and model calculations indicated that the liquid-phase reaction was instantaneous or at least very fast, with Ha number over 100.