By-products generated by agro-industries are important alternatives to low cost sources for food enrichment and nutritional components in the human diet, mainly because of their high levels of fiber and protein. The aim of this study was to develop cookies enriched with by-products applying multicomponent mixture experiments (MME) to perform partial replacement of wheat flour by cassava, peach palm and soy bean flour. The maximum level (component proportion = 1) of each variable was 20% (related to total formulation) of the corresponding wheat flour. Flour characteristics, cookie properties and parameters were evaluated. PF had the highest fiber content (32.60 g kg−1), CF got the highest carbohydrate content (78.44 g kg−1) and SF had the highest protein (29.03 g kg−1) and fat (16.14 g kg−1) contents. We have thus established that it is possible to obtain cookies enriched with low cost by-products that have high fiber content and provide sensorial acceptability. A formulation of MME (33.40%CF+33.40%SF+33.40%PF) was the most appropriate one when simultaneous responses to crude fiber and protein contents, besides the hedonic score, were evaluated. The fiber content increased from 1.87 g kg−1 (control) to 5.95 g kg−1 in enriched cookies. Flours used for enriching cookie production had potential to be utilized as a functional ingredient for food products.