During the coronavirus disease-2019 (COVID-19) pandemic, there was a lack of access to outpatient facilities for other diseases. Conversely, few studies have reported changes in clinical features of idiopathic nephrotic syndrome (INS) in children before and after the COVID-19 pandemic. Thirty-two children with primary INS, who were admitted to four Showa University-affiliated hospitals between January 2017 and December 2022, were enrolled in this retrospective study. Children were divided according to the onset of INS into a post-COVID-19 group (onset in 2020-2022, n = 25) and a pre-COVID-19 group (onset in 2017-2019, n = 32). We compared the clinical characteristics and features of initial INS between two groups. In the post-COVID-19 group, these patients had interval between noticing symptoms of INS, such as edema and INS diagnosis was significantly longer (7days versus 3.5days; p = 0.0047), and had significantly raised serum LDL cholesterol levels at the time of INS diagnosis than in the pre-COVID-19 group (314mg/dL versus 260mg/dL; p = 0.028). Likewise, steroid-resistant nephrotic syndrome was significantly more common in the post-COVID-19 group [32% (n = 8) versus 6% (n = 2); p = 0.016]. A correlation analysis revealed a moderate positive correlation between the interval from symptom to diagnosis and LDL cholesterol (r = 0.460015, p = 0.0003). Children with INS after the COVID-19 pandemic showed a longer time between noticing symptoms of INS and diagnosis, increased serum LDL cholesterol and more steroid resistance than before the pandemic.