Abstract The intercalation reaction of hydrated K+ ions into the layered structure of 2H-NbS2 was studied using in situ X-ray diffraction. A structurally complex intercalation mechanism was observed showing several highly one-dimensionally disordered intercalated phases. A quantitative modelling of the disorder in K x (H2O) y NbS2 is presented allowing a complete understanding of the intercalation mechanism.