Summary The high proportion of seed coat of legume lupins results in big milling lose during kernel flour production, though the seed coat could be value‐added as human food. The physicochemical and nutritional properties and antioxidant capacities of seed coats of six Australian sweet lupin cultivars grown at two locations were evaluated. Results showed that genotype, environment and their interaction were significant for seed coat percentage, proximate composition, dietary fibre content, polyphenols and antioxidant capacities. Strong correlations between seed coat lightness and polyphenol content were found. A comparison using multivariate analysis of the seed coat properties showed clear separation based on growing sites. This study indicates the enormous potential of Australian sweet lupin seed coat as an ‘antioxidant dietary fibre’ food source. The results could also benefit to breed varieties with desirable levels of nutrients and phytochemicals. Six new Australian sweet lupin cultivars grown at two locations were sampled to examine the genotypic and environmental effects on compositional and physicochemical properties of lupin seed coat. Valorisation strategies of the seed coat were discussed.