The aim of this study was to determine the amino acid content and in vitro protein digestibility of breakfast cereals and evaluate their protein quality using in vitro protein digestibility-corrected amino acid score (PDCAAS) methods. Statistically big differences were found in the proportions of essential amino acids between breakfast cereals. Higher protein digestibility was found in samples containing rice and corn than those containing oats. The first limiting amino acid score (AAS) in 6 out of 12 samples was methionine + cysteine, in 4 out of 12 samples was lysine, and in 2 out of 12 samples was tryptophan. According to the first limiting AAS, the in vitro PDCAAS ranged from 0.19 +/- 0.01 to 0.86 +/- 0.02 in breakfast cereals. When we evaluated the first limiting AAS, lysine, methionine+cysteine and tryptophan predominantly determined PDCAAS. As a result, the PDCAAS, which is an indicator of protein quality, was generally low in breakfast cereal products.