Two strain crosses of mycoplasma-free broiler breeders were allocated to three treatment groups, each group consisted 10 replicates and each replicate comprised of 10 females and 2 males. These g roups were fed one of three treatment diets for 112 days: 0, 35mg or 50mg tylosin phosphate/kg diet. Fertility and hatchability of the groups were recorded. Significant improvement in fertility and hatchability by 4.0 and 3.8 per cent respectively in birds fed 35 mg tylosin phosphate/kg diet and by 7.2 and 6.2 per cent respectively in birds fed 50 mg tylosin phosphate/kg diet were observed.