Background: Despite the fact that, ferritin is commonly regarded as a representation of total body iron reserves; its predictive value is also connected to COVID-19 severity. COVID-19 disease can manifest itself in pregnant women in a variety of ways. Comorbid conditions have a significant impact on the progression of COVID-19 severity. Several studies have showed that, serum ferritin level was associated with severity of COVID-19 infection. So, we conducted this study to evaluate the comparison of mean serum ferritin levels between non-severe and severe COVID-19 infection groups during third trimester of pregnancy. Objectives: The aim of this study is to compare the mean serum ferritin levels between non-severe and severe COVID-19 infection groups in third trimester of pregnancy. Methods: This cross-sectional study was carried out in Department of Obstetrics and Gynaecology, COVID-19 Unit, BSMMU and DMCH. Sampling method was purposive. Total 154 cases were included in this study after matching eligibility criteria. After collecting intravenous blood, serum ferritin level was measured. Results: Among 154 cases, 24.7% cases were asymptomatic, 40.3% cases were mild, 24.7% cases were moderate and 10.4% cases were severe COVID-19 infection during third trimester of pregnancy. The non-severe COVID-19 infection group consisted of 100 cases of asymptomatic and mild COVID-19 infected patients, with a mean serum ferritin level of 51.48 ng/ml. The severe COVID-19 infection group consisted of 54 cases of moderate and severe COVID-19 infected patients, with a mean serum ferritin level of 478.37 ng/ml. The independent samples t-test revealed a p-value of ≤0.05 (0.0000000002), when comparing the mean values of these two groups. Conclusion: Serum ferritin level rises significantly in severe COVID-19 infection during third trimester of pregnancy.