Diabetes mellitus is a metabolic disease that has become a public health problem. It is characterized by hyperglycemia. The aim of this book is to present the antihyperglycemic, antioxidant, antialzheimer and cytoprotective effects of extracts from two plants from northeastern Algeria: Rosmarinus officinalis (RO) and Thymus numidicus (TN). In the first stage, phytochemical investigation of extracts from several fractions of the two plants revealed polyphenol and flavonoid content, antioxidant activity, antiglycation power, the ability of the extracts to inhibit the enzymes -amylase and acetyl choline esterase, and to elucidate the most effective fraction of the two plants on the activity of carbohydrate metabolism enzymes. Secondly, two in vivo experiments were carried out: the first to assess the hypoglycemic and anti-hyperglycemic effects on normal and glucose-loaded rats, and the second to study the dose-dependent effect of the two plants' extracts on carbohydrate metabolism.