Objective To investigate the association between serum alkaline phosphatase (ALP) and type 2 diabetes mellitus (T2DM) with nonalcoholic fatty liver disease (NAFLD). Methods A total of 599 patients with T2DM who were hospitalized in Department of Endocrinology, Affiliated Hospital of Jiangsu University, from July 2016 to December 2018 were enrolled as subjects. According to the presence or absence of NAFLD, the patients were divided into NAFLD group with 286 patients and non-NAFLD group with 313 patients, and according to the results of abdominal ultrasound, the patients with NAFLD were divided into mild group with 111 patients, moderate group with 105 patients, and severe group with 70 patients. General clinical data were compared between groups. The independent samples t - test was used for comparison of normally distributed continuous data between two groups, and an analysis of variance was used for comparison between three groups; the Mann-Whitney U test was used for comparison of non-normally distributed continuous data between two groups, and the Kruskal-Wallis H test was used for comparison between three groups; the chi-square test was used for comparison of categorical data between groups. Pearson correlation analysis and Spearman correlation analysis were used to investigate the correlation between ALP and clinical indices, and a logistic regression analysis was used to investigate the influencing factors for NAFLD. Results Compared with the non-NAFLD group, the NAFLD group had significantly higher proportion of patients with history of hypertension ( χ 2 =7.864, P < 0.05), systolic blood pressure ( t =-2.226, P < 0.05), diastolic blood pressure ( t =-3.800, P < 0.05), body mass index (BMI) ( t =-11.842, P < 0.05), waist circumference (WC) ( t =-9.150, P < 0.05), fasting insulin (FINS) ( Z =-6.173, P < 0.05), fasting C-peptide ( t =-5.419, P < 0.05), serum uric acid ( t =-4.957, P < 0.05), low-density lipoprotein cholesterol ( t =-2.702, P < 0.05), triglyceride ( Z =-9.376, P < 0.05), total cholesterol (TC) ( t =-3.016, P < 0.05), Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) ( Z =-5.794, P < 0.05), alanine aminotransferase (ALT) ( Z =-6.737, P < 0.05), aspartate aminotransferase (AST) ( Z =-4.389, P < 0.05), gamma-glutamyl transpeptidase (GGT) ( Z =-7.764, P < 0.05), and ALP ( t =-2.833, P < 0.05), as well as significantly lower age ( t =2.184, P < 0.05) and high-density lipoprotein cholesterol ( Z =-5.273, P < 0.05). The severity of NAFLD (mild, moderate or severe) was positively correlated with age ( r s =0.140, P < 0.05), BMI ( r s =0.239, P < 0.05), WC ( r s =0.222, P < 0.05), FINS ( r s =0.191, P < 0.05), HOMA-IR ( r s =0.218, P < 0.05), ALT ( r s =0.188, P < 0.05), AST ( r s =0.279, P < 0.05), GGT ( r s =0.202, P < 0.05), and ALP ( r s =0.361, P < 0.05). In the patients with T2DM and NAFLD, ALP was positively correlated with HbAlc ( r =0.149, P < 0.05), fasting plasma glucose ( r =0.146, P < 0.05), HOMA-IR ( r s =0.132, P < 0.05), TC ( r =0.151, P < 0.05), ALT ( r s =0.210, P < 0.05), AST ( r s =0.192, P < 0.05), and GGT ( r s =0.297, P < 0.05). The logistic regression analysis showed that ALP was an influencing factor for NAFLD in patients with T2DM (odds ratio=1.013, 95% confidence interval: 1.004-1.023, P < 0.05). Conclusion Elevated serum ALP is a risk factor for T2DM with NAFLD and is closely associated with hyperglycemia, insulin resistance, and hyperlipemia, and ALP may play a role in the development and progression of T2DM and NAFLD.