In vitro α-glucosidase inhibitory activity of unroasted, and medium, dark and very dark roasted robusta coffee was studied. Coffee extracts significantly inhibited the enzyme activity in a dose-dependent way. The inhibitory activity was well correlated with the degree of roast. Coffee components were separated by gel permeation chromatography into low (1 < MW < 6 kDa), intermediate (15 < MW < 60 kDa) and high (MW > 100 kDa) molecular weight fractions, which were analyzed for the α-glucosidase inhibitory capacity. Only fractions obtained from dark and very dark roasted coffee exhibited inhibitory effect. When the same fraction was obtained from coffee presenting different roasting degree, changes in α-glucosidase inhibition extent were observed. This was attributed to compositional changes within each fraction as induced by roasting. Coffee extracts and their fractions exerted a mixed-type to competitive inhibition against α-glucosidase and these mechanisms are consistent with the complexity of coffee composition.