Lablab bean [Lablab purpureus (L.) Sweet] has been shown to be the most promising bean to grow in mixture with corn (Zea mays L.) to increase silage crude protein concentration in northern environments. This research was conducted to determine the impact of corn and lablab bean plant densities on mixture silage quality. The experiment was conducted near Arlington and Lancaster, WI and harvested when corn was at 2/3 kernel milkline. Eight combinations of corn-lablab bean from each location were ensiled in 0.5-L glass jars for 30 days, then analyzed for pH and fermentation products. Bean proportions in mixtures ranged from 0 to 380 g/kg DM, and were affected by both bean and corn plant density in the field. Silage pH ranged from 4.07 to 3.83 with high-density corn and lablab bean (80/80 thousand plants/ha) having the highest pH and solo corn (40 000 plant/ha) lowest pH. Lactic acid concentration was also affected by the amount of lablab bean. The lowest corn-highest bean density (20/80 thousand plants/ha) had the greatest lactic acid concentration (72 g lactic acid/kg DM), while corn with no bean (60/00 thousand plants/ha) had the lowest (47 g lactic acid/kg DM). The trend was for higher pH and greater lactic acid concentrations as the proportion of bean in mixtures increased. This is likely associated with greater buffering capacity as bean proportions increase, extending fermentation but having minimal impact on silage pH. All mixtures were well preserved based on silage pH and profiles of fermentation products.