This dataset contains 85,933 individual records of length measurements for 112 freshwater fish species collected from Cambodian inland freshwater ecosystems. The data can be used to establish length-length models that can be applied to standardized length measurements in support of fisheries biology, ecological studies, and fish stock assessment. Measurements include total length (TL), standard length (SL), and fork length (FL), reported in centimeters (cm). SamplingFish were sampled across the upper Mekong–3S River system, Tonle Sap Lake, and Tonle Sap River using arrow-shaped traps, the dai fishery, stationary gillnets, and samples from local landing sites and markets. Sampling was conducted during 2020–2021 and covered both wet and dry seasons. Each record represents one individual fish. Data FileFish_Length_TL_SL.csvFish_Length_TL_FL.csvFish_Length_FL_SL.csv Variables: Species (Scientific name), TL.cm (Total Length in centimetre), SL.cm (Standard Length in centimetre), FL.cm (Fork Length in centimetre), and Data_collection (sampling method). Cite this database as: Uy S., Chhuoy S., Pin K., Chhorn S., Sup M., Soem S., Chan B., Chandra, S., Hogan, Z.S. & Ngor P.B. (2026) Length-length relationships for freshwater fishes in Cambodia. Cambodian Journal of Natural History, 2026, 42-57.