Objective · To investigate the correlation between the levels of serum thyroid hormones or free triiodothyronine/free thyroxine（FT3/FT4） ratio and non-alcoholic fatty liver disease (NAFLD) in euthyroid patients with type 2 diabetes mellitus (T2DM). Methods · The consecutive medical records of inpatients with T2DM were collected at the Department of Endocrinology and Metabolism in Shanghai Ninth Peoples Hospital February 2016 to July 2017. Totally 256 euthyroid T2DM patients were enrolled after excluding subjects with thyroid dysfunction, other liver diseases and excess alcohol consumption. The diagnosis of NAFLD was based on abdominal ultrasonography. Patients were divided into T2DM with NAFLD group (92 cases) and without NAFLD group (164 cases). Matching function in R language was performed for 1:1 match (age, sex and body mass index) between two groups. Multiple linear regression and Logistic regression analyses were used to evaluate the correlation between the levels of thyroid hormones or FT3/ FT4 ratio and NAFLD. Results · There were 92 subjects in each group after matching data. The results indicated that levels of FT3, total triiodothyronine (TT3) and FT3/FT4 ratio in T2DM with NAFLD group were higher than those of T2DM without NAFLD group as well as total cholesterol (TC), triacylglycerol (TAG), low density lipoprotein cholesterol (LDL-C), glutamic-pyruvic transaminase (GPT), glutamic-oxaloacetic transaminase (GOT) and γ-glutamyl transferase (γ-GT) (all P<0.05). Multivariate linear regression analysis revealed that FT3 level and FT3/FT4 ratio were linearly positive with GPT and GOT levels, respectively (both P<0.05). TT3 was linearly positive with GPT, GOT and γ-GT levels. Logistic regression analysis showed that FT3 was independently associated with NAFLD inT2DM patients (P0.018). Furthermore, the ROC curve analysis verified the accuracy ofFT3/FT4 ratio for predicting NAFLD in T2DM patients (P0.005). Conclusion · In euthyroid T2DM patients, FT3 level and FT3/FT4 ratio positively correlate with NAFLD. Meanwhile, FT3/FT4 ratio might be useful for predicting NAFLD.