Abstract: Microneedles composed of micron-sized needle arrays are a novel transdermal drug delivery strategy with minimally invasive penetration through the stratum corneum barrier, thus efficiently delivering drugs to the corium layer. Currently, most microneedles use immediate release polymer materials as the matrix, which rapidly dissolves to release the drug without achieving sustained release, making it unfit for long-term drug delivery or treatment of chronic diseases. Sustained-release microneedles can retain the drug in the biodegradable matrix for slow release, with prolonged therapeutic effects and reduced dosing frequency, thus helping to enhance patient compliance. This review categorizes major designs of sustained-release microneedles, and summarizes the biomedical applications of sustained-release microneedles, including long-term contraception, long-acting treatment for hair loss, prolonged antimicrobial effects, long-term relief of postoperative pain and treatment of tumor, with a prospect of future research directions in sustained-release microneedles technology.