Background: Glucose metabolism is frequently impaired in patients with Cushing’s syndrome (CS), which is caused by chronic exposure to glucocorticoid excess. Inflammation plays a central role in the pathophysiology of diabetes mellitus (DM). The present study aimed to investigate the potential associations of inflammatory blood cell parameters, including white blood cell (WBC) count, neutrophils count, neutrophilic granulocyte percentage (NEUT%), lymphocyte count (LYM), lymphocyte proportion (LYM%) with diabetes mellitus in Cushing’s syndrome patients. Materials and Methods: This cross-sectional study was performed in Zhongshan Hospital, Fudan University, China. A total 150 patients with Cushing’s syndrome were retrospectively screened from 2017-2019. The demographic, clinical data, and blood samples were documented (lipids, adrenal, glucose, inflammatory blood cell parameters). Statistical analyses were carried out by using SPSS software package version 13.0. Results: The prevalence of diabetes mellitus was 38.7% in Cushing’s syndrome. Patient with DM had higher WBC, neutrophils, NEUT% levels than patients without DM (P < 0.05). As the NEUT% increased, there was a step-wise increase in glucose and HbA1c level. Additionally, in the multivariate logistic regression, NEUT% was an independent risk factor for the development of DM, regardless of gender, age, BMI, triglyceride and 12MN cortisol level (OR=2.542, 95%CI 1.337-4.835, P<0.001). Conclusions: In conclusion, elevated NEUT% level was associated with diabetes in patients with Cushing syndrome. The neutrophils granulocyte percentage may be used as a new predictor for diabetes in Cushing’s syndrome patients.