Mastitis is a major disease in dairy cattle of Ethiopia. The objectives of this study were tornidentify aerobic bacterial pathogens, estimate the incidence of mastitis, identify thernassociated risk factors and assess drug resistance patterns of bacterial isolates in heifersrnmastitis. The study was conducted for eight months and a total of 124 quarters werernexamined to detect clinical mastitis and subclinical mastitis by udder physicalrnexaminations and the California mastitis test (CMT) respectively. California mastitis testrnpositive milk samples were used to isolate and identify bacteria. The study revealed thatrnthe incidence rate of mastitis per gland month at risk was 39.45%. The incidence ofrnmastitis was found to be affected by management system, udder hygiene, dry cowrntherapy and lactation stage (p < 0.05). The percentage of CMT positive glands thatrnremained positive after a month and the percentage of CMT negative glands thatrnremained negative after a month were 57.14% and 79.91% respectively. Staphylococcusrnaureus (25.11%), Coagulase negative staphylococci (CNS) [14.70%] and Streptococcusrnspecies (14.70%) were the predominant bacteria. In the present study, out of eight in vitrornantimicrobials used; gentamycine (0%), kenamycin (0%), ampicillin (62%), penicillin Grn(89%), chloramphinicol (8%), Cefoxitin (16%), tetracycline (84%) and trimethoprimrn(8%), showed resistance to heifer mastitis pathogens. Gentamycine and chloramphinicolrnwere the most effective antibiotics among all the tested ones. Finally due to the highrnresistance level detected in the study, it was believed that it is necessary to set uprnantimicrobial resistance surveillance programmes in the country. It was also concludedrnthat the prevalence of Staphylococcus aureus warrants serious attention, the applicationrnof antibacterial agents earlier before calving may help to reduce the incidence of mastitisrnduring the early lactation period.