The kinetics of phase demixing in an aqueous two-phase system (ATPS) consisting of PEG/sodium citrate, with various PEG molecular weights (2000, 4000, and 6000) was investigated at 25 degrees C. The rate of demixing of the phases (top/bottom) is essential to scale up the aqueous two-phase extraction (ATPE) process. The individual phase physical properties like density, viscosity, and interfacial tension are highly dynamic with the phase composition, and are responsible for the demixing of phases. Hence, in the present study, the variation of physical properties with phase compositions in terms of tie line length (TLL) was considered for the analysis of the rate of demixing of phases. The effect of the volume ratio of the phases (top/bottom) on the kinetics of phase separation also studied since the dispersed phase holdup in the mixture influences the rate of demixing. The higher TLL with a salt-rich phase as continuous phase showed higher reduction in demixing time when than low TLL at the volume ratio of <1. Based on the analysis, empirical correlations were proposed for top and bottom phase demixing rate in terms of Morton's number, volume ratio, and TLL. The coefficients and constants from the literature and the present correlations were estimated through regression analysis. The developed correlation predicted the demixing rate with lower AARD (+/- 7%) for both the phases. The proposed correlation was accurate and simple in predicting the demixing rate of PEG/sodium citrate ATPS at 25 degrees C.