This experiment was conducted to confirm the effect of sodium hydroxide spray treatment and to know whether the physiological changes occur, when spray treated rice straw was fed to cattle during long-term period. Fifteen male Holstein cattle weighing about 200 ㎏ were randomly assigned to three treatments (untreated, 5% NaOH and 10% NaOH treated), Daily weight gain was slightly but not significantly increased by the 5% sodium hydrorcide treatment, bur decreased by the 10% sodium hydroxide treatment. Feed utilizations were improved by the sodium hydroxide treatments and it would be explained by the reduced daily DM intake. Serum Na and K levels were not increased by either 5% or 10% sodium hydroxide treatments of rice straw, There were no consistent or significant changes in the serum concentrations of other minerals betwesn untreated and sodium hydroxide-treated rice straw fed groups. Although plasma bicarbonate concentrations were elevated by the sodium hydroxide treatment, metabolic alkalosis was unlikely to be generated. Total VFA concentrations in the rumens were slightly increased but not significantly different by the sodium hydroxide treatments.