Amaranth–oat composites were developed using gluten free amaranth flour containing essential amino acids and minerals with oat products containing β-glucan, known for lowering blood cholesterol. Amaranth–oat composites were used in sugar cookies for improving their nutritional and physical qualities. The physical properties of amaranth–oat composites, and their cookies and doughs were compared with amaranth or wheat flour alone. The pasting viscosities of amaranth–oat 3:1 composites were similar to amaranth flour alone, and they were all higher than wheat flour. The study showed amaranth and its composites had more viscous properties and improved water holding capacities compared to wheat flour. Differences were also found in geometrical properties and texture properties of the dough and cookies. However, the amaranth–oat cookies were acceptable in color, flavor and texture with no significant differences in sensory qualities compared to wheat flour cookies. Also, the cookies using amaranth–oat composites had enhanced nutritional value with gluten free uniqueness that could be useful for functional foods.