<p>Body fluid/tissue identification (BFID) is a fundamental forensic task for determining the origin of biological evidence such as blood, saliva, and semen. While traditional BFID methods rely on enzymatic, immunological, or spectroscopic methods, the emergence of RNA profiling has expanded its capabilities to not only identify body fluid/tissue but also, to some extent, assign them to specific contributors. This review focuses on three fundamental biological characteristics of RNA molecules that underpin their applications: specificity, stability, and polymorphism (length, sequence, and expression variations). Furthermore, research progress in RNA-based fluid/tissue analysis is discussed, highlighting the applications of these properties and addressing the remaining challenges. This article provides a comprehensive overview of the principles and current state of RNA analysis for forensic body fluid/tissue identification and contributor assignment.</p>