Background: COVID-19, as a contagious infectious disease, can affect many systems and cause changes in inflammatory and hematological parameters. This study aims to research the effects of hematological and inflammatory parameters on prognosis of the disease and the duration of hospitalization. Methods: 186 patients aged 15-92 with positive COVID-19 PCR test results and a control group consisting of 187 healthy individuals with similar characteristics in terms of age and gender are included in the study. Age, gender, hematological variables, and inflammatory parameters of the patients on the 1st and 5th days of hospitalization were recorded retrospectively. Results: The mean age of the patient’s group was 47.0 ± 18.4 years and 54.3% were male. WBC, lymphocyte count, and platelet count were statistically lower in the patient group compared to the control group, while MPV, NLR, and PLR levels were higher. On the 5th day of the patient follow-up compared to admission day, it was observed that the neutrophil count and MPV level were lower; However, the platelet count and ferritin level were statistically higher. While there was a significantly positive correlation between the duration of hospitalization and the 5th day D-dimer (r = 0546, p < 0.001) and ferritin (r = 0.568, p < 0.001); there was a negative correlation between the duration of hospitalization and admission day lymphocyte count (r = 0.256, p = 0.006) and the 5th day lymphocyte count (r = 0.325, p < 0.001). Conclusion: Increased levels of ferritin and D-dimer and decreased count of lymphocyte are among important factors affecting the duration of hospitalization for COVID-19 patients. Furthermore, we think that neutrophil count and MPV levels are low and platelet count and ferritin levels are high during the course of the disease, so these parameters can be used as prognostic indicators of the disease.