B complex vitamins play an important role in the metabolism of carbohydrates, proteins and fats. The aim of this study was to determine the effects of B complex vitamins administered by exogenous route on rumen protozoa, hematological and blood biochemical parameters in clinically healthy cattles. Thirty cattles aged between 6 to 18 months, and breeding in Afyonkarahisar Province and surrounding regions were studied.  Ten clinically healthy animals served as control group. Twenty study group animals were given 10-20 ml B complex vitamins, 3 times during 3 days, by intramuscular route.  Clinical (body temperature, pulse and respiration rates, rumen contractions), hematological (total leukocyte count, erythrocyte count, hemoglobin and hematocrit measurements), and serum biochemical (aspartate aminotransferase, glucose, total protein, albumin) parameters along with rumen protozoa status were measured in all animals. Regarding hematological parameters, there was no significant difference between the study groups in term of time intervals (P> 0.05). The mean values of WBC, RBC, neutrophils, HGB, HTC, MCV, MCH and MCHC were different between the case and the control groups (P< 0.05), but the mean values of lymphocytes, monocytes, and basophils were not different (P> 0.05). AST, SDH, ALP enzyme levels averaged within the reference limits, but were significantly higher in the case group (P< 0.05). Consequently,  the use of B complex vitamins have proved to be of great benefit as it did not caused adverse effects on the digestive system at certain intervals in cattle.