Reference intervals for blood biochemical analytes and packed cell volume are useful to veterinarians and conservation programs for monitoring the health of threatened species. Populations of the critically endangered Chinese three-striped box turtle, Cuora trifasciata (Bell, 1825), are heavily depleted in the wild because of overharvesting; and many individuals are now maintained in captive breeding programs. Reference intervals of biochemical analytes and packed cell volume were established for individuals of this species held in a captive breeding program at Kadoorie Farm and Botanic Garden, Hong Kong. Blood samples were obtained from 86 healthy individuals from a captive population during annual health examinations between 2006 and 2010. Packed cell volume and 17 biochemical analytes were measured, and data were analyzed using both multivariate and univariate statistical analyses. Significant differences in eight analytes between males and females were identified. Ten analytes were found to increase or decrease significantly with the body weight of the turtles. The reported plasma reference intervals, based on 2.5th and 97.5th percentiles, may serve as benchmarks for clinical assessment and conservation of this critically endangered species.