Abstract: A polyelectrolyte complex (PEC) made up of poly(di-allyl di-methylammonium chloride) and poly(styrene sulphonate) polyelectrolytes has been synthesised and used for the immobilisation of phosphomolybdate (PMo), [PMo12O40]3- nanoclusters. The material is characterised by FTIR, powder XRD, SEM, TEM and UV-Visible DRS spectroscopy. It was found that the PMo clusters are intact in the hybrid and are present as nanoaggregates within the layers of PEC. The amount of PMo present in the hybrid is estimated from thermal measurements and the optical band gap energy of the material is found to be in the semiconductor region. The presence of negatively charged PMo clusters helped in almost complete adsorption of cationic dyes, methylene blue and rhodamine B. The PMo/PEC hybrid has shown to follow Langmuir adsorption isotherm in case of both the dye molecules. Graphic abstract: Polyelectrolyte complex immobilised with Keggin-type phosphomolybdate ions showing efficient adsorption of Methylene Blue and Rhodamine B dye molecules.[Figure not available: see fulltext.]. © 2020, Indian Academy of Sciences.