Endothelial dysfunction is directly involved in consequence of various metabolic syndromes such as diabetes and hypertension. In this study, we investigated the preventive effects of two ark clams [ark shell (AS, Scapharca subcrenata) and granular ark (GA, Tegillarca granosa)] on endothelial dysfunction induced by a high-fat diet. Wistar rats were divided into four groups as follows: control (normal diet), HF (high-fat diet), AS (high-fat diet + 5% AS powder), and GA (high-fat diet + 5% GA powder) for 12 weeks. AS and GA diets enhanced vascular reactivity of the rat thoracic aorta and significantly increased expression levels of vascular relaxation-related proteins (p-Akt-ser473 and p-eNOS-ser1177). Ark clam supplement reduced endothelin-1 expression level, as compared to the HF group. Additionally, AS and GA showed a trend of improving insulin sensitivity compared to HF. Our results suggest that AS and GA enhance vascular reactivity and ameliorated endothelial dysfunction induced by a high-fat diet. © 2020, The Author(s).