Biosimilar products of filgrastim have become available for improved sustainability of cancer care; however, the real-world safety profile remains unknown. The purpose of this study was to clarify the adverse events associated with filgrastim originator and its biosimilar using the Japanese Adverse Drug Event Report (JADER) database. Adverse event reports submitted to the Pharmaceuticals and Medical Devices Agency between 2014-2018 were extracted. We calculated the reporting odds ratio and 95% confidence interval for each adverse event. We obtained 584 reports of adverse events associated with filgrastim originator and 102 reports with its biosimilar. Signals were detected for bone marrow failure and febrile neutropenia with both filgrastim originator and its biosimilar; whereas those for drug resistance and hypoxia only involved filgrastim originator, and those for interstitial lung disease only involved its biosimilar. The safety profiles of filgrastim originator and its biosimilar were partly different. Further studies are needed to confirm these findings.