Trichomonas gallinae is the causative agent of canker in pigeon. This work was carried out to investigate in the vitro and in vivo efficacy of aqueous water extract of garlic (AGE) on the growth of T. gallinae infecting pigeons compared to those of metronidazole (MTZ). MTZ and AGE were added, at different concentrations, to glucose-serum broth medium containing 1 × 104 trophozoites/ml. In the in vivo experiment, 48 squabs were grouped into four groups. The first group (gr. I) was not infected and not treated. Each squab of the other group was infected with 1 × 104 trophozoites. The second group (gr. II) was infected and not treated. On day 0, the third group (gr. III) was treated with MTZ (50 mg/kg BW) and the fourth group (gr. IV) was treated with AGE (200 mg/kg BW) for seven successive days in drinking water. In vitro study revealed that the MLC, 24, 48, and 72 h post treatment were 50, 25, and 12.5 μg/ml, respectively, for MTZ and 75, 50, and 50 mg/ml, respectively, for AGE. Garlic (200 mg/kg BW) had the highest antitrichomonal effect and shortened course of treatment of pigeons from 7 days in gr. III to 5 days. Squabs in gr. II suffered from macrocytic hypochromic anemia, whereas squabs in grs. III and IV showed normal blood pictures. Serum total protein, albumin, and globulin were increased, whereas AST, ALT, and the total cholesterol were decreased in grs. III and IV when compared to those of gr. II. Pigeons protected with AGE showed increased body weight and reduced mortality percentage than the other groups. Our results indicated that garlic may be a promising phytotherapeutic agent for protection against trichomoniasis in pigeons.