•Diversity in fiber composition of amaranth, buckwheat and quinoa was recorded.•Fiber polysaccharides of pseudocereals are rich in pectins and xyloglucans.•Fiber polysaccharides have various claimed biological functions and health effects.•Fiber polysaccharides and fractions have formulated in food products such as breads.•Effects of polysaccharides and fractions also relate to impurities such as phenolics. Seeds of amaranth (Amaranthus spp.), buckwheat (Fagopyrum esculentum and F. tataricum) and quinoa (Chenopodium quinoa) become popular foods due to their attractive health effects. Cell wall polysaccharides are the major components of dietary fiber and significantly contribute to diverse health effects of the grains. This review summarizes chemical and physical structure, biological functions and food uses of the cell wall polysaccharides and fractions as fiber components from the 3 pseudocereals. The properties and uses of the polysaccharides and fractions are compared with those of fiber polysaccharides from common sources such as fruits and vegetables. Overall, the fiber polysaccharide composition of the pseudocereals is more similar to that of fruits and vegetables than to that of cereals. The fiber polysaccharides showed a range of biological functions such as antioxidation, anticancer and immunomodulation. The fiber polysaccharides of amaranth, buckwheat and quinoa have potential to be used in formulations of functional foods.