Pericardial effusion is a serious problem in companion animals. Neisseria spp. are considered commensal microorganisms of the oral cavity in dogs and cats and are usually isolated from human wounds resulting from bites on these animals. This article presents a clinical case of a cat with hydropericardium, the cause of which was Neisseria animaloris. Identification of the pathogen in the pericardial sac fluid was performed using the MALDI-TOF method. This is the first report on a documented case of pericardial effusionin a cat triggered by Neisseria animaloris bacterial infection in feline medicine, emphasizing its novelty using the MALDI-TOF method.