In this report, sclerosing sialadenitis of the sublingual salivary glands is described in a three-yearold, male, mixed breed cat. Sublingual masses were dissected and removed under dissociative anaesthesia. The patient had recovered completely at two months post-surgery. The two soft and pale red masses were 1.5 x 1 x 0.5 cm in size. Histologically, it was observed that the masses were covered with stratified squamous epithelium containing large numbers of salivary glands and ducts in the collagen-rich loose connective tissue. Scattered lymphocyte infiltrations were observed in the connective tissue. Mild to severe lymphocyte infiltration was seen between salivary glands. Some glands exhibited severe fibrosis, epithelial destruction and atrophy. To the best of our knowledge, this is the first report of sclerosing sialadenitis in a cat. Chronic sclerosing sialadenitis (Kuttner's tumour) is a condition that has been defined in humans. Histological findings similar to those of Kuttner's tumour were observed in this case, and dense plasma cell infiltrations suggested immune-mediated plasmacytic disease, which has been reported as a potential aetiology of Kuttner's tumour. Corticosteroid therapy was not attempted, and the patient was treated successfully using surgical excision.