The aim of this study was to evaluate the effects of medicinal herbs, essential oils, and monensin on performance, ruminal fermentation parameters, blood metabolites and behavior of Holstein calves. Sixty-six dairy calves fed colostrum until day 3 of age and then randomly assigned to one of six treatments including: 1) control (starter feed without herb essence), 2) control + thyme, 3) control + eucalyptus, 4) control celery, 5) control + monensin, 6) control + peppermint commercial oil. All calves assigned to experimental diets received 2.5 percent of the starter feed (As fed). Calves were fed 6 liter milk daily (two times a day) until weaning. Feed intake was monitored weekly but average daily gain was measured two times per week. Skeletal growth was measured on the first (d 1) and last day (d 70) of study. To assess blood metabolite and rumen fermentation parameter, rumen fluid and blood were collected on day 35 and 70 of study. To calculate digestibility of experimental diets, feed and fecal samples were collected before and after weaning period. Similar to digestibility, animals' behavior was observed before and after during this period. Herbal supplementation has no significant effects on dry matter intake, daily gain, skeletal growth and feeding behavior. Except two cases, rest of the rumen fermentation parameters and blood metabolites did not affected by treatments. In this respect, starter feed contained thyme decreased serum alanyn aminotransferase (ALT) enzyme compared to control treatment after weaning (P 0.05). Serum betahydroxy Butyric acid (BHBA) was higher in calves fed commercial oil starter than the control diet (P 0.05). Results has shown that 2.5 percent of herbal essence in starter feed (as fed) did not affect performance and behaviors of dairy calves but lead to change some of rumen fermentation and blood parameters. Keywords : Herbal essence, performance, Rumen Fermentation, Blood Metabolite, Calves