Background Hypertension is the major public health concern; leading to cardiovascular disease. It is associated with alteration in hematological parameters which may lead to end-organ damage. Thus, this study aimed to compare hematological parameters between hypertensive and normotensive adult groups in Harar, eastern Ethiopia. Methods A comparative cross-sectional study was conducted from January to March, 2020 at Jugel and Hiwotfana Specialized University hospital, Harar, eastern Ethiopia. Convenient sampling technique was used to recruit 102 hypertensive patients from the two hospitals and 102 apparently healthy blood donors. Participant's socio-demographic and clinical information were collected using pre-tested structured questionnaire. Blood sample were collected and analyzed by Beckman Coulter DxH 500 analyzer for complete blood count. The data were entered and analyzed using SPSS version 23. Independent t-test and Mann Whitney u-test was used for comparison between groups. Spearman's correlation was used for correlation test. P values less than 0.05 was considered as statistically significant. Result 102 hypertensive and 102 healthy controls were enrolled in this study. The median ± IQR value of white blood cell (WBC) count, hemoglobin (Hgb), hematocrit (HCT), red cell distribution width (RDW) and mean platelet volume (MPV) were significantly higher in hypertensive group compared to apparently healthy control group. Additionally, RBC (red blood cell) count, HCT and RDW showed statistically significant positive correlations with systolic and diastolic blood pressure. WBC count and RDW were significantly and positively correlated with body mass index (BMI). Platelet (PLT) count had a significant but negative correlation (r = -0.219, P = 0.027) with duration of hypertension illness while MPV showed positive and significant correlation (r = 0.255, P = 0.010). Conclusion The median values of WBC, Hgb, HCT, RDW and MPV were significantly higher in hypertensive patient compared to apparently healthy individuals. Hence, it is important to assess hematological parameters for hypertensive individuals which may help to prevent complications associated with hematological aberrations. However, further studies are required to understand hypertensive associated changes in hematological parameters.