The effects of single dose medroxyprogesterone acetate (MPA) applications on serum estradiol 17-beta, progesterone, growth hormone levels and their receptors in mammary glands, development of feline mammary fibroepithelial hyperplasia and the efficacy of progesterone hormone for suppression of first estrus in queens were investigated. Crossbred 20 queens were divided into two equal groups. Initiation and the end of the first heats were detected by clinical signs and vaginal smears. At the 1st day of estrus (Day -1) blood and mammary gland tissue samples were taken from the cats. Following day (Day 0), treatment (MPA) group received 100 mg MPA, control group received same dose physiologic saline solution intramuscularly. Blood samples were collected at intervals of 3 day during the first heat and at 10 day intervals thereafter for a period of 4 months. Two other mammary gland samples were collected at intervals of 45 days after Day 0. Serum progesterone levels were significantly (P < 0.05) higher on days 2, 30, 50, 60 70, 90 for treated group than control group cats; serum estradiol 17-beta levels were significantly (P < 0.05) higher on days 20, 30, 40, 50, 70, 100 for control than MPA group of the study. Growth hormone could not be detected throughout the study both in serum and in receptors of the mammary tissue samples. Clinically feline mammary fibroepithelial hyperplasia occurred in a cat and ultrasonography was performed when the lesion first noticed. Tissue samples had significantly higher estrogen receptor labelling for control than MPA group. Highly extensive and dense progesterone receptor positive labelling were observed in all tissue samples. It was concluded that MPA was effective to suppress estrus in cats. The incidence of feline mammary fibroepithelial hyperplasia (FMFH) was small. There can be higher incidence of occurring FMFH when used more cat population.