Oregano (Origanum vulgare) is a rich source of natural phenolic antioxidants and has potential to be a source of nutritional ingredients for functional foods. Herbs such as oregano have long been used in food preservation and in traditional medicine in the treatment of common ailments and have potential for positive modulation of oxidation-linked diseases such as diabetes. One of the potentially important components of anti-diabetic activity by oregano extract is mild amylase inhibition by phenolic antioxidants to help contribute towards management of hyperglycemia. Previously, we reported the ability of rosmarinic acid, one of the principal phenolic components of oregano, to inhibit porcine pancreatic amylase (PPA) activity. Here, we investigated the effect of 50% ethanol extracts of eleven phenolic antioxidant-rich oregano clonal lines on the activity of PPA in vitro. To this end, we analyzed extract total soluble phenolic content by the Folin-Ciocalteu reagent method, rosmarinic acid (RA), protochatechuic acid (PA), quercetin, and p-coumaric acid (pCA) contents by HPLC, antioxidant activity as 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging, and PPA-inhibitory activity by incubation of the enzyme with clonal oregano extracts and characterization of the activity of the phenolic-bound enzyme. Clonal oregano extracts inhibited the activity of PPA in vitro by 9-57%. Amylase inhibition by oregano extract was associated with extract total phenolic content and RA, quercetin, PA, and pCA content, as well as extract antioxidant activity and protein content. Our finding that clonal oregano extracts can inhibit PPA supports a potential new functionality for oregano as an anti-hyperglycemic agent. This provides an opportunity for a food-based strategy for modulation of starch breakdown to glucose, which could contribute to the management of hyperglycemia and diabetes complications in the long term.