Field peas (Pisum sativum L.) have been cultivated for centuries for human consumption, due to the high nutritional quality of pea protein. However, during the last years, increasing demand for field peas for livestock feeding has developed a market in Canada, Europe, and the U.S. Therefore, as is the case with some feed ingredients, differences in soil, varieties, agronomic practices, and growing method may change the nutritional characteristics of the peas as well as the digestibility of nutrients. Besides that, differences in the particle size of field peas may change the digestibility of nutrients. Therefore, the objective of this experiment was to test the hypothesis that the standardized ileal digestibility (SID) of crude protein (CP) and amino acids (AA) in field peas is affected by the particle size of the field peas and the region where the field peas were grown.