As alfalfa (Medicago sativa L.) is the most profitable hay crop in the USA, there is interest in producing alfalfa as an alley crop in agroforestry. Little information is available on alfalfa when grown as an alley crop. Field experiments were conducted near Stockton, MO in 2003 and 2004. Treatments consisted of alfalfa grown in open plots and in plots that were alley cropped between black walnut trees (Juglans nigra L.) planted in 24.4-m rows (wide) and 12.2-m rows (narrow). In the tree plots, one sample was taken beneath the dripline and one in the center of the alley. Plots were sampled for three harvest cycles each year. Alfalfa herbage was cut 5 cm above the soil surface from two 1.0-m2 areas within each plot. Data were taken on yield, crude protein, acid detergent fiber (ADF) and neutral detergent fiber (NDF), and maturity as measured by mean stage by count. Alfalfa yield in the open plots was similar to yield in the center of the wide alleys in every harvest but one. Yield in the open plots and the center of the wide alleys was greater than under the dripline and narrow alleys for all three harvests both years. Alfalfa tended to mature faster in the open plots and in the centers of wide alleys compared to the dripline and narrow alleys. Crude protein tended to be similar or greater in the open and centers of wide alleys compared to the dripline and narrow alleys in every harvest but the last harvest in 2004. Yields were low at that harvest due to lack of rainfall. No consistent differences were found for ADF and NDF. Alfalfa yield was reduced and maturity was delayed when grown near the dripline or in alleys with narrow tree spacing.