It is clear that providing sufficient fiber in dairy cattle diets has most positive effects on improvement of rumen ecosystem and feed intake efficiency. In semiarid countries such as Iran providing forage requirement of cattle is limited. So it is better to use plants with low water requirement, high growth rate and high forage yield per hectare. Canola (Brassica napus L.) recently has received consideration as a forage source for livestock (Lancaster et al., 1990). Canola is reasonably widely adapted and performs well in many areas of Iran. In addition to its low water requirements and high growth rate, its cultivation season is well matched with environmental condition in Iran. The main objective of this study was to evaluate effect of replacing maize silage with canola silage (as dry matter %) on Holstein dairy cow performance.