Background: Hemoglobin A1c (HbA1c) measures blood glucose over a period of 2–3 months, and its level is closely related to the risk of complications. Several factors affecting HbA1c levels have not been studied. This study mainly focused on the relationship between HbA1c levels and complete blood count (CBC) parameters. Objectives: This study aimed to analyze the relationship between HbA1c levels and CBC parameters in patients with type 2 diabetes mellitus (T2DM) and to evaluate the association of CBC parameters with abnormal HbA1c levels and diabetic complications. Methods: This was a retrospective study of 385 Saudi patients with T2DM aged ≥18 years attending King Khalid University Hospital (KKUH) primary care clinics. Patients with type 1 diabetes mellitus, hematological diseases, infections, or allergies were excluded. AnElectronic System for Integrated Health Information (e-SiHi)was used to collect data, which were analyzed using SPSS 22 using t-test and analysis of variance, with P <0.05 considered significant. Results: This study showed that the mean patient age was 59±13 years, with no significant difference between the sexes. In addition, the mean duration of disease was 10 years, and the mean HbA1c level was 8.5±1.9 %. CBC values were averaged according to their mean values, except for the erythrocyte sedimentation rate (ESR) (36±27 mm/hr) which was higher than the normal value (1.0–25 mm/hr). Conclusion: This study showed an association between HbA1c levels and duration of T2DM and hemoglobin. The progression of diabetic complications was related to CBC changes a high ESR was associated with the incidence of diabetic nephropathy and increased white blood cell count with neuropathy, vasculopathy, and nephropathy. Among all complications, vasculopathy occurred more frequently with each increase in HbA1c values.