The effect of different amounts of whey protein concentrate (50–150 g kg−1), low and high methoxyl pectin (5–15 g kg−1) on the rheological, thermal, structural properties and sensory quality of mashed potatoes prepared from dried mashed potatoes flakes was investigated. The response surface technique was used to analyse the effects of whey protein concentrate and pectin simultaneously on the consistency index, flow behaviour index, apparent viscosity and Casson plastic viscosity. Both whey protein concentrate and pectin decreased the consistency of the mashed potatoes weakening its structure in all concentrations assayed. Results suggest that whey protein concentrate interacts with high methoxyl pectin through non-covalent interactions. Based on the sensory evaluation results, up to 100 g kg−1 whey protein concentrate with 15 g kg−1 of low methoxyl pectin and 15 g kg−1 of high methxyl pectin could be incorporated to dried mashed potatoes flakes without losing significantly the sensory quality of the product.