Abstract: Background and Objective: Boldenone is an androgenic steroid that progresses the development and nourishment change in nourishment creating creatures. In most nations around the world, this anabolic steroid is illegal for human employments and for meat generation because it was created for veterinary utilize. As of late, it is utilized by bodybuilders in both low season and pre-contest, where it is well known for expanding vascularity whereas planning for a weight training challenge. So, the current study was aimed to investigate the possible prophylactic effect of rosemary extracts response of to boldenone induced blood alterations, cardiac toxicity, injury and oxidative stress, in male rats. Materials and Methods: A total of 20 adult male rats were divided into 4 groups (1st group was control, 2nd group was treated with rosemary, 3rd group was boldenone group include rats that injected intramuscular boldenone (5 mg kg–1 b.wt./week) for 4 weeks, 4th group was post treated group include rats that injected intramuscular boldenone every week for 4 weeks and then treated with rosemary for another 4 weeks). Results: Intramuscular injections of boldenone induced a significant increase in serum lactate dehydrogenase (LDH), creatine kinase (CK), creatine kinase isoform (CK-MB), myoglobin, malondialdehyde (MDA) and cardiac tissue injury while a significant increase in serum glutathione (GSH), superoxide dismutase (SOD) and catalase activity as compared with their relative values in the control group. These findings explained the common phenomena in athletics and bodybuilders who suffer from problem in cardiovascular system, cardiac toxicity following injection with some steroids drugs as boldenone to build muscles or for enlarge lips or cheeks or breast or buttocks as well as included in many cosmetics. Conclusion: Rosemary extracts could scavenge free radicals and produce beneficial effects against boldenone induced damage in heart, oxidative stress and blood alternations.