The purpose of this study was to assess the effects of Soybean Oil Calcium soap (SO-Ca) on blood profiles, rumen fermentation properties, microbial populations, and the performance of Bali's calves. Using a randomized block design, three treatment groups of six replications each contained 18 calves. Treatments included 0% SO-Ca (control/T0), 5% SO-Ca (T1), and 10% SO-Ca (T2). The diet of each treatment (Concentrate mix and Napier grass) used in the study was formulated based on the usual ration given to the cattle with energy levels approximately the same between treatments. Analysis of variance was used to assess the data and the Tukey Test was then used to determine whether there were any significant differences between the treatments. The findings demonstrated that the addition of SO-Ca up to 10% lowered (p≤0.01) the total protozoa population but had no effect on the overall bacterial population. The fraction of propionate increased (p = 0.03) and the concentration of NH3 tends to rise (p = 0.10). However, the addition of SO-Ca up to 10% reduced the proportion of acetate (p = 0.045), butyrate (p = 0.03), C2/C3 ratio (p = 0.02) and tended to reduce valerate (p = 0.1) and methane estimation (p = 0.06). Blood metabolites, performance, and rumen pH were comparable between treatments. The addition of SO-Ca tends to lower the cholesterol level (p = 0.10). In conclusion, the addition of SO-Ca improves propionate proportions and reduces methane estimation as well as cholesterol levels, which are both positive impacts on rumen fermentation.