Background: The circulating levels of Cyr61 (also known as CCN1) may prove to have great clinical value in the diagnosis, monitoring and prognosis of many disorders in humans. However, the reference intervals (RIs) for this analyte in human subjects have not previously been well established. Therefore, establishing RIs and determining the distribution of circulating Cyr61 levels are very important for future clinical studies and could provide an orientation value for exploring its clinical usefulness. Methods: The Cyr61 levels in 2,514 healthy Chinese Han subjects (1,250 males and 1,264 females, aged 18 - 88 years, recruited from 4 hospitals in Shanghai and Fujian) were measured with a sandwich ELISA (R&D Systems, USA). The RIs were determined in a manner consistent with the Clinical and Laboratory Standards Institute guidelines. Results: The levels of serum Cyr61 showed a non-Gaussian distribution. A statistically significant difference was observed between the males and females such that the median level of Cyr61 in the males was significantly higher than that in the females. Furthermore, the Cyr61 levels significantly increased with age in the female group whereas no difference was observed among the different age groups among the males. The RIs for serum Cyr61 were 3.3 - 184 pg/mL and 5.0 - 182 pg/mL in females aged 18 - 45 and 46 - 88 years, respectively. The RI for serum Cyr61 was 4.0 - 198 pg/mL in the males. Conclusions: The RIs for serum Cyr61 were established among Chinese Han individuals. The effects of age and gender on the distribution characteristics of serum Cyr61 were studied, revealing that the RIs were gender and, in females, age-specific, which may suggest that a female hormone, estrogen plays a role in the regulation of Cyr61 expression in vivo.