The ESR absorption spectrum of Mn 2+ ions at Zn positions has been studied in the incommensurate phase of Rb 2 ZnCl 4 . It is known that Rb 2 ZnCl 4 crystals exhibit an incommensurate phase between temperatures T i = 303 K and T l = 192 K. The form and the temperature dependence of ESR spectra are in good agreement with the predictions of the phase soliton theory. The parameters h 1 and h 2 determining the magnetic resonance field show, as expected, a power law as a function of the temperature. A modified superposition model was used to estimate the modulation amplitude of the incommensurate phase, and the principal axis of the zero field splitting D.