<p>Rare sugars such as L-fucose, L-rhamnose, and D-altrose possess diverse biological activities and increasing industrial relevance in pharmaceuticals, food, and biomaterials. Microbial exopolysaccharides (EPS) are a renewable and structurally diverse source of these sugars; however, their natural abundance in EPS is often limited. Emerging evidence shows that environmental stress—such as osmotic pressure, pH variation, nutrient limitation, and temperature shifts—can significantly alter EPS composition and promote the incorporation of rare sugars. This review provides a comprehensive overview of the occurrence and biological significance of these uncommon monosaccharides in bacterial polysaccharides. It highlights the influence of environmental stress on microbial metabolism and EPS structure, with emphasis on stress-induced changes in gene expression, sugar nucleotide biosynthesis, and glycosyltransferase regulation. Biotechnological strategies, including stress-optimized fermentation, co-culture systems, metabolic engineering, and synthetic biology, are also discussed as tools to enhance the biosynthesis and incorporation of structurally distinct sugar residues into the polysaccharide matrix. By integrating insights from microbial physiology, metabolic control, and process engineering, this review underscores the potential of environmental stress as a sustainable and versatile approach for producing rare sugar-enriched EPS. Future research opportunities and current knowledge gaps are also addressed, with a focus on systems-level understanding and translational applications.</p>