The anti-inflammatory effect of Spirulina platensis (S. platensis) on induced cutaneous immediate-type hypersensitivity in dog was evaluated by using five healthy dogs. The experiments were consisted of 3 periods. At the first time, dogs were received nothing before induced cutaneous immediate-type hypersensitivity reaction using histamine and compound 48/80 intradermally. On the second time, dogs were received dry matter of S. platensis, which compose of phycocyanin being a major compound, for 10 days before they were performed the induction. Then dogs were withdrawn for 14 days, and received antihistamine drug (Hydroxyzine HCl) for 10 days before the induction was done. The immediate reaction was subjectively scored by measuring the diameters of the lesions in millimeters. Skin biopsies were performed and tissue sections were stained to determine the inflammatory cell infiltration and mast cell degranulation in each time of induction. Diameter sizes of wheal, numbers of inflammatory cell in the second and third times were lower than control group significantly, but no significant difference between second and third time. Numbers of non-degranulated mast cell in the time of S. platensis were significantly higher than control and antihistamine. It might from S. platensis that could inhibit mast cell degranulation. This study suggested that S. platensis had an efficiency to inhibit induced cutaneous immediate-type hypersensitivity reaction as same as antihistamine drugs. Hence, if the used of S. platensis in treatment of allergic skin disease was developed, it would be an effective alternative way of curing allergic skin disease.