Objective: Serum YKL-40 level is elevated in patients with several malignancies. This study was designed to assess the correlation between serum YKL-40 and the corresponding tissue expression in endometrial cancer (EC). Materials and Methods: Preoperative serum levels of YKL-40 were measured by enzyme-linked immunosorbent assay (ELISA) from 41 patients with EC, 27 patients with uterine myoma, and 30 healthy women. YKL-40 protein expression in tissue was determined by immunohistochemistry for patients with EC and patients with uterine myoma. Results: Median preoperative serum YKL-40 level was 157.2μg/l (range 76.0 - 301.2) in EC compared with 86.6 μg/l (range 69.3 - 191.1) in uterine myoma, and 86.2 μg/l (range 52.1 - 201.1) in healthy women (p < 0.05). Of 41 patients with EC, 26 patients with elevated serum YKL-40 level statistically differed from the remaining 15 patients with normal serum YKL-40 level with respect to FIGO Stage, tumor grade, washing cytology, and serum CA125 (p < 0.05). In multivariate analysis, elevated serum YKL-40 significantly correlated with FIGO stage(p < 0.05) and tumor grade (p <0.01). The percentage of positive YKL-40 tissue staining was higher in EC patients (34.1%, 14/41) than in uterine myoma patients (11.1%, 3/27) (p < 0.05) and was lower than that of elevated serum levels in EC (26/41, 63.4%) (p < 0.05). Conclusions: The elevated preoperative serum YKL-40 is related to stage and histologic grade of EC. The discordance between serum and tissue level of YKL-40 in EC indicates intrauterine tumor may not be the only source of serum YKL-40.