In July 2023, H5N1 Highly Pathogenic Avian Influenza (HPAI) infection was confirmed in cats at two private animal shelters in Seoul, Korea. All infected or deceased cats had consumed raw duck-based pet food, and HPAI virus was detected in the product. Genetic sequencing showed a 99.9–100% match between the virus in the pet food and that in infected cats, supporting foodborne transmission. The manufacturing plant had suspended sterilization in May 2023, raising concerns about inadequate safety protocols. Emergency measures included a product recall, surveillance of 286 pet cats, and monitoring of 102 shelter animals, all of which tested negative. No human infections; even so, authorities emphasized personal hygiene and wildlife monitoring. This case highlights the need for stricter safety controls in pet food production and the importance of a One Health approach in managing zoonotic risks. Given the close contact between companion animals and humans, preparedness for potential cross-species transmission should be reinforced.