The influence of modern soil ameliorants such as anionic potassium humates (PHums) and cationic poly(diallyldimethylammonium chloride) (PDADMAC) as well as their interpolymer complexes (IPCs) on rheological behavior of water-saturated kaolinite was studied. Modification of kaolinite with anionic biologically active and bio-stimulating PHums was shown to result in a decrease of storage modulus G0′ and shear stress amplitude τ0 corresponding to linear viscoelasticity region as well as storage modulus Gcross′ and shear stress amplitude τcross at crossover point by 0.5 – 1.0 order of magnitude. Modification of the clay with cationic PDADMAC was accompanied by the opposite effect, that is, an increase in the above rheological characteristics by 1.5 – 2.0 orders of magnitude. PDADMAC/PHums IPCs with the molar ratio of cationic and anionic groups in the range 0.1 – 10 demonstrated the influence on the rheological parameters in the same manner as individual PDADMAC. This result was considered as the original procedure to provide simultaneous addition of stabilizing PDADMAC and biologically active PHums. In this case the reinforcing action of PDADMAC on the kaolinite is fully realized and the weakening action of PHums is fully suppressed. For individual polymers, the results are discussed in terms of kaolinite structural transformations caused by the interaction of charged macromolecules with negatively charged clay particles. For IPCs/kaolinite samples, rheological behavior was attributed to the exchange reactions between IPCs and clay particles. The data obtained are important for predicting the mechanical properties of wet clay soils modified with polymers and IPCs, as well as optimizing methods for introducing bio-stimulating and anti-erosion polymer additives into soils. © 2024 Elsevier B.V.