Background: COVID-19 pneumonia is responsible for the latest pandemic. Usage of pulmonary computed tomography (CT) scan is known to be an important method in the diagnosis of COVID-19. Here, we aimed to evaluate the relationship between CT severity score and capillary blood oxygen saturation in patients with COVID-19 infection. Methods and material: This is a cross-sectional study performed in 2020 on patients with COVID-19 infection. All patients underwent pulmonary CT scan and CT severity score was calculated. The initial capillary oxygen saturation by the time of admission was also collected. Data were collected and analyzed. Results: A total number of 270 patients diagnosed with COVID-19 infection entered the study. The initial mean capillary oxygen saturation was 89.65 ± 8.09%. The mean score in patients was 15.16 ± 8.08. We also indicated that 27 patients had hypoxia by the time of admission and these patients had significantly higher CT severity scores (p = 0.001). Diabetes mellitus (p = 0.001), hypertension (p = 0.001), and chronic obstructive pulmonary disease (COPD) (p = 0.03) and totally having an underlying disease (p < 0.001) were significantly associated with decreased capillary oxygen saturation. Patients with hypertension (p = 0.001) and patients with the previous medical disease (p = 0.01) had significantly higher CT severity scores than others. There was a significant reverse relationship between CT severity score and capillary oxygen saturation (r = −0.44, p < 0.001). Conclusions: We showed that there was a significant reverse relationship between CT severity score and capillary oxygen saturation which has great clinical importance. Furthermore, we indicated that previous medical history could also play an important role in CT severity score.