Background <p>Periprosthetic joint infection (PJI) is a challenging complication of joint arthroplasty, and fungal pathogens account for only 1% of all such cases. Among these, <i>Aspergillus</i>-related PJI is exceedingly rare, and to date, no standardized treatment guidelines have been established.</p> Case presentation <p>An 86-year-old woman presented with right knee pain 14 years after total knee arthroplasty. PJI was suspected based on the initial characteristics of the joint fluid, prompting surgical irrigation and debridement. Although the initial bacterial cultures before antibiotic administration were negative, fungal growth was observed in two intraoperative samples. Detailed analysis identified the causative organism as <i>Aspergillus penicillioides</i> after 8 weeks. The patient achieved stabilization of C-reactive protein levels with voriconazole treatment, without undergoing implant removal.</p> Conclusions <p>We present a case of <i>Aspergillus penicillioides</i>-related PJI, which, to our knowledge, has not been previously reported in PJIs. This case highlights the diagnostic challenges posed by rare fungal PJIs, particularly those caused by <i>Aspergillus penicillioides</i>. It is important to maintain clinical vigilance for rare fungal PJIs, as certain species, such as <i>Aspergillus penicillioides</i>, are slow-growing and difficult to identify with standard culture techniques.</p> Clinical trial number <p>Not applicable.</p>