The objective of this study was to investigate the effect of a partial substitution of soybean meal with field pea (Pisum sativum) in Holstein lactating dairy cow diets on dry matter intake, milk yield and composition, blood metabolites, rumen ammonia-N concentration and pH. Eighteen lactating Holstein cows were randomly assigned into three groups based on parity, days in milk, and milk yield. Flaked field peas replaced soybean meal (SBM) at the levels of 0.0, 33 and 66% (P-0, P-33 and P-66, respectively) and were fed to the animals for 33 days. Dry matter intake, milk yield, milk fat and protein content, blood metabolites, rumen ammonia-N concentration and pH were not significantly (P<0.05) affected by the diets. The results of this study demonstrated that field pea could safely replace soybean meal up to 66% in the diet of high-producing dairy cows.