The effect of salt blocks with biotin content (300mg/kg and 100mg/kg, HBFB and LBFB) was examined on serum biotin concentrations and the incidence of the hoof diseases in 217 dairy cows. These salt blocks were fedad-libitumover the course of one year. One year from the commencement of this trial, the serum biotin concentrations of these cows were significantly (P<0.001, P<0.01) elevated in the HBFB and LBFB groups: 589±432pg/mlto 1, 101±1, 058pg/mland 473±250pg/mlto 667±554pg/ml, respectively. The number of cows with hoof disorders declined significantly (P<0.001) in the HBFB group, from 62/121 cows (51.2%) in the initial examination to 25/121 cows (20.7%) after one year. In normal cows, the incidence of hoof disease was significantly (P<0.05) fewer in the HBFB group (8/59 cows: 13.6%), than that in the non-HBFB group (17/54 cows: 31.5%). These results suggest that HBFB elevates the serum biotin concentration, decreases the frequency of hoof disorder, and prevents hoof disease in dairy cows.