Poly-D-glutamic acid sodium salt is a synthetic, water-soluble polymer composed of D-glutamic acid units linked by peptide bonds. It is the enantiomer of the naturally occurring poly-L-glutamic acid. Its key structural feature is the high density of carboxylate groups along the polymer backbone, which confers strong anionic and polyelectrolyte properties. In the pharmaceutical field, it is primarily investigated as a novel and functional excipient. Its applications include serving as a biodegradable drug delivery carrier for sustained or controlled release formulations, a mucoadhesive agent to enhance drug residence time, and a stabilizer for protein or peptide drugs. Its biocompatibility and ability to form hydrogels make it suitable for biomedical uses. In materials science, it acts as a functional copolymer building block for creating biodegradable polymers, hydrogels for tissue engineering scaffolds, and environmentally friendly materials. As a synthetic polymer derived from a non-natural enantiomer, it offers advantages like resistance to enzymatic degradation by common proteases, which can be tailored for specific release profiles. Safety and regulatory status for specific pharmaceutical applications are typically under research and development.