In this study, to assess the diagnostic value for mastitis in dairy cows, change of acute phase proteins(haptoglobin and serum amyloid A) concentrations in milk and sera of dairy cows were measured. 50 dairy cows were used in this experiment and divided into two groups. The first group was the healthy dairy cow group whose milk contained less than 2.0${ imes}$10$^$5/ somatic cell counts(n=5). The second group was the mastitis-dairy cow group whose milk counted higher than 5.0${ imes}$10$^$5/ somatic cell counts(n=45). The concentration of haptoglobin and serum amyloid A in milk and sera from these two groups were determined by Tridelta range haptoglobin kit and serum amyloid A kit. The concentration of haptoglobin in the milk from first group was undetectable value and that of the second group was 124.0$mu extrm{g}$/$mell$. And the concentration of haptoglobin in serum of the first group was 32.0$mu extrm{g}$/$mell$ and that of the second group was 214.4$mu extrm{g}$/$mell$. The concentration of serum amyloid A in the milk from first group was 0.32$mu extrm{g}$/$mell$ and that of the second group was 17.7$mu extrm{g}$/$mell$. And the concentration of serum amyloid A in serum of the first group was 5.1$mu extrm{g}$/$mell$ and that of the second group was 25.8$mu extrm{g}$/$mell$. It was concluded that concentration of haptoglobin and serum amyoid A in milk and serum may be was to discriminate between normal and mastitic milks.