Abstract: The aim of the current study was to evaluate the increasing doses of OEO extracted from Berastagi orange peels on performance, rumen fermentation and blood metabolites in fattening Bali cattle. Fifteen male Bali beef cattle of similar age 1.5-2 years and initial body weight (194.4±22.31 kg) were used in a Completely Randomized Block Design (RCBD) for 90 d. The doses of OEO supplementation ware applied by oral infusion. Dose of the OEO supplementation treatments were: 0 ppm (basal diet + 0 ppm OEO/kg DMI), 200 ppm (basal diet + 200 ppm OEO/kg DMI), 400 ppm (basal diet + 400 ppm OEO/kg DMI), 800 ppm (basal diet + 800 ppm OEO/kg DMI) and 1200 ppm (basal diet + 1200 ppm OEO/kg DMI). The basal diets were formulated based on protein and TDN content of 13 and 65% with swamp grass: concentrate ratio of 60: 40%. Swamp grass and concentrate were given separately. The animal were fed twice a day, morning and afternoon. Oral infusion of OEO treatments were given after the animal fed a morning of concentrate using disposable syringe. The obtained result showed that the increasing doses of OEO did not influence on final BW, DMI, ADG and FCR. OEO supplementation was significantly (p<0.05) decreased on ruminal NH3-N, molar proportion of acetate and ratio acetate to propionate, whereas total VFA and molar proportion of propionate tended to increase. Supplementation of OEO at the dose 800 ppm and 1200 ppm was tended to decrease of total VFA and molar proportion of propionate. There were no effect of increasing dose of OEO on pH, molar proportion of butyrate, valerate, iso-valerate. Serum concentration of glucose, total triglycerides, albumin were no changed by increasing dose of OEO, but serum total protein tend to increased (p<0.15) by OEO supplementation. Moreover, supplementation of OEO decreasing serum concentration of total cholesterol, LDL, urea and BUN and increasing serum concentration of HDL. Our results suggest that supplementation of berastagi orange oil at dose 400 ppm could be considered as suitable feed additives to manipulate rumen microbial fermentation and to improve blood metabolites in fattening Bali cattle.