Injectable urethral bulking agents composed of synthetic and biological biomaterials are minimally invasive treatment options for stress urinary incontinence (SUI). The development of an ideal urethral bulking agent remains challenging because of clinical concerns over biocompatibility and durability. Herein, the mechanical and biological features of injectable urethral biomaterials are investigated, with particular emphasis on their future potential as primary and secondary treatment options for SUI. A literature search for English language publications using the two online databases was performed. Keywords included "stress urinary incontinence", "urethral bulking agent" and "injectable biomaterial". A total of 98 articles were analysed, of which 45 were suitable for review based on clinical relevance and importance of content. Injectable biomaterials are associated with a lower cure rate and fewer postoperative complications than open surgery for SUI. They are frequently reserved as secondary treatment options for patients unwilling or medically unfit to undergo surgery. Glutaraldehyde cross-linked bovine collagen remains the most commonly injected biomaterial and has a cure rate of up to 53 %. Important clinical features of an injectable biomaterial are durability, biocompatibility and ease of administration, but achieving these requirements is challenging. In carefully selected patients, injectable biomaterials are feasible alternatives to open surgical procedures as primary and secondary treatment options for SUI. In future, higher cure rates may be feasible as researchers investigate alternative biomaterials and more targeted injection techniques for treating SUI.