Introduction: The aim of this study was to investigate various biochemical and hematological parameters in patients with type 2 diabetes mellitus (T2DM) and compare those with non-diabetic subjects (control group). Subjects: The study was conducted on 405 subjects (ages ranging from 26-65 years old; sex matched) who were classified into two groups: diabetic (n=205 subjects; males-105, females-100) and non-diabetic subjects (n=200; males-100, females-100). The study was carried out during the period of November 2016 to April 2017 in the Department of Clinical Laboratory Sciences at the College of Applied Medical Science Al-Dawadmi, Shaqra University in Saudi Arabia (with the collaboration of the General Hospital Al-Dawadmi). Methods: The following various parameters were assessed for all subjects: body mass index (BMI), systolic and diastolic blood pressure (SBP-DBP), fasting blood sugar (FBS), serum glutamic pyruvic transaminase (SGPT), alkaline phosphatise (ALP), total cholesterol (T. Ch), triglyceride (TG), low-density lipoprotein (LDL), high density lipoprotein (HDL), hemoglobin (HB), red blood cell count (RBC), hematocrit (Ht), mean corpuscular volume (MCV), mean corpuscle hemoglobin concentration (MCHC), mean corpuscular hemoglobin (MCH), red cell distribution width (RDW), platelet count (Plt), mean platelet volume (MPV), platelet distribution width (PDW), total white blood cell count (WBC), lymphocyte count (L), neutrophil count (N), eosinophil count (E), monocyte count (M), basophil count (B), neutrophil/lymphocyte ratio (N/L), and platelet/lymphocyte ratio (P/L). Results: The results showed an increase in the mean values of SGPT, alkaline phosphatase, urea, serum creatinine, total cholesterol, triglyceride, and LDL in the T2DM group relative to the control group. Meanwhile, the mean value of HDL was significantly decreased in the T2DM group compared to the control group (p 0.05), but the mean values of PDW and MPV were significantly higher in the T2DM group compared to the control group (p0.05). Conclusion: In diabetes mellitus type 2 patients, certain biochemical and hematological changes are distinct from healthy subjects. It is important to follow up and monitor these parameters carefully in diabetic patients. Peer Review Details Peer review method: Single-Blind (Peer-reviewers: 02) Peer-review policy Plagiarism software screening?: Yes Date of Original Submission: 30 September 2017 Date accepted: 05 November 2017 Peer reviewers approved by: Dr. Lili Hami Editor who approved publication: Dr. Phuc Van Pham