Cisplatin, which kills cancer cells mainly through DNA crosslinking, has been widely used as a first-line chemotherapeutic agent although it also causes severe side effects. To improve anticancer outcomes, various types of cisplatin-based nanomedicines have been developed, either through direct incorporation or coordination of cisplatin within nanoparticles (NPs). During the formulation and characterization of cisplatin-loaded NPs, quantitative determination of cisplatin is crucial for both clinically used and newly developed NPs. While NPs facilitate cisplatin delivery, the use of different nanomaterials inevitably complicates its determination and increases the cost of quantification. Currently, there is still a significant demand for an accurate, simple, and cost-effective method to determine cisplatin in NPs, which would facilitate the screening and quality control of cisplatin-based nanomedicines. This review aims to discuss the main strategies for quantifying cisplatin, following a summary of the main types of cisplatin-loaded NPs. Application examples of cisplatin determination in NPs are provided, and the key features of each quantification strategy are compared. In addition, NP-based electrochemical sensors are included as an emerging approach for characterizing cisplatin loaded in NPs. Rational selection of an appropriate cisplatin determination method for NPs according to the quantification principle and specific drug-delivery settings is highly recommended.