Abstract Background Previous research indicates that COVID-19 infection may have a role in triggering IgA nephropathy (IgAN). However, limited research has explored the clinical implications of COVID-19 infection in individuals already diagnosed with IgAN. Objective This study aimed to determine whether COVID-19 infection independently affects the subsequent trajectory of kidney function in IgA nephropathy patients. Design A single-center cohort study. Participants The study included 199 patients diagnosed with IgA nephropathy. Methods The COVID-19 infection status was determined using a combined method: a questionnaire and the Health Code application, both administered at the end of 2022 in northern China. Kidney function trajectory was assessed by the estimated glomerular filtration rate (eGFR), calculated based on serum creatinine levels measured during follow-up outpatient visits. Primary Outcome The primary endpoint of interest was the eGFR trajectory. Result Out of the 199 participants, 75%(n=181)reported a confirmed SARS-CoV-2 infection, determined through antigen or PCR tests, accounting for 79% (n=143) of the infected patients. A significant majority (98%) experienced mild to moderate symptoms. Over a median follow-up period of 10.7 months post-COVID-19 infection, notable clinical events included gross hematuria in 30 patients (16.6%), which normalized within an average of three days. Additionally, a two-fold increase in proteinuria or progression to the nephrotic range was observed in 10 individuals (5.5%). No cases of acute kidney injury (AKI) were noted. COVID-19 exposure was associated with an absolute change in eGFR of 2.98 mL/min/1.73 m² per month (95% CI, 0.46 to 5.50). However, in a fully adjusted model, the estimated changes in eGFR slope post-COVID-19 were -0.39 mL/min/1.73 m² per month (95% CI, -0.83 to 0.06, P = 0.088) included the possibility of no significant effect. Notably, a higher rate of kidney function decline was primarily observed in patients with a baseline eGFR below 45 ml/min/1.73m² (-0.56 ml/min/1.73m² [-1.11 to -0.01], P = 0.048). Limitations In the cohort, there were few instances of severe COVID-19 cases. The absence of long-term follow-up outcomes was observed. Conclusion Overall, mild to moderate COVID-19 infection does not appear to significantly exacerbate the subsequent decline in kidney function among IgAN patients, particularly in those with preserved baseline kidney function.