Objective: To evaluate the effect of topically applied hyaluronic acid gel (hyaluranon) on gingivitis in diabetic rats. The evaluation based on clinical, histological, and immunohistochemical analysis. Materials and Methods: The present study included seventy rats were included in this study, sixty rats were divided into two main groups according to treatment modality, group I involved thirty rats treated with topical HA, while group II involved thirty rats left untreated. Furthermore groups I and II subdivided into subgroups Ia, IIa were sacrificed on the seventh day, and subgroups Ib, IIb were sacrificed was sacrificed on the day fourteen, negative control compromised five healthy rats, and positive control group compromised five diabetic rats. Harvested gingival specimens were fixed in formalin, then embedded in paraffin wax, and serially sectioned at 4μm for immunohistochemical assessment using Prolyl 4 Hydroxylase A1(P4HA1). Results: Immunohistochemical evaluation using P4HA1 revealed a significant difference between all groups.