In the past years, the relevance of introducing ionic liquids (ILs) has been shown as phase-forming components of aqueous biphasic systems (ABS), which allow the tailoring of polarity differences between the coexisting phases. Although investigations on the IL chemical structure and polymermolecularweight have been carried out, the use of mixtures of polymers can also be seen as a way of tailoring their two-phase formation ability and separation performance, which was not attempted earlier. In this work, we investigate novel ABS composed of cholinium-based ILs and mixtures of polymers, namely polyethylene glycol (PEG) of 400 and 2,000 g·mol-1, at differentmole fractions, as a way of tailoring the formation of ABS and their separation performance. The respective liquid-liquid phase diagrams were determined, and their ability to separate a set of alkaloids (caffeine, theophylline and theobromine) appraised. An increase on the PEG 2000mole fraction favors the formation of ABS. However, this does not follow a monotonous trend, where mole fractions of PEG 400 up to 0.3 do not display significant impact on the two-phase separation capability. Among the studied alkaloids, nicotine preferentially partitions to the IL-rich phase, while the remaining alkaloids majorly partition to the polymer-rich phase. Different selectivity patterns were verified, depending on the cholinium-based IL used and water content at the IL-rich phase. Overall, by using mixtures of polymers it is possible to decrease the viscosity of the coexisting phases and their toxicity impact, without losing their formation and separation capacities, by the addition of PEGs of lower molecular weight.