Postnatal systemic steroids are known to increase the risk of developing retinopathy of prematurity (ROP). However, whether the total dosage and type of postnatal systemic steroids are related to the development and severity of ROP in premature infants remains unclear. This study was conducted to identify the risk factors for ROP and investigate the relationship between photocoagulation (PC)-demanding severe ROP and the postnatal dosage of any type of systemic steroids. A total of 75 infants born at <28 weeks of postmenstrual age (PMA) were enrolled. The number of PC procedures for ROP was evaluated as the objective variable. This study analyzed the following independent variables: gestational age; birth weight; sex; Apgar scores; duration of mechanical ventilation; duration of nasal intermittent positive pressure ventilation; mean saturation and mean oxygen concentration administration until 36 weeks of PMA; total accumulation dosage of hydrocortisone, dexamethasone, and systemic steroids; dosage number of times of erythropoietin; total dosage of red cell concentrates (RCC); incidence of necrotizing enterocolitis (NEC) and focal intestinal perforation; sepsis; bronchopulmonary dysplasia (BPD); and intraventricular hemorrhage (IVH). Logistic regression was used to estimate the relative risk (odds ratio (OR)) associated with risk factors for PC-demanding severe ROP. Compared with infants in the non-PC group, PC-treated infants had younger gestational age, longer mechanical ventilation periods, and higher dosage of systemic steroids and dexamethasone. Multivariate logistic regression analysis revealed total dosage of systemic steroids as the only risk factor for PC-demanding severe ROP. Based on receiver operating characteristic (ROC) curve analysis, a cutoff value of 8.95mg/kg of postnatal systemic steroid administration was identified as a useful marker to predict PC-demanding severe ROP. By focusing on the method of systemic steroid administration and avoiding excessive doses for infants born at <28 weeks of PMA, preventing the development of severe ROP is possible.