Canola meal is one of the most widely used protein sources in animal feeds. It has an excellent amino acid profile and it is rich in vitamins and essential minerals. Many experiments have been conducted on the value of canola meal for dairy cows. Excellent and often improved milk production has resulted from the use of canola meal as a main protein source. Canola meal provides an important contribution to both rumen microbial protein needs as well as to the digestible amino acids required for animal growth and lactation. Canola meal possesses an excellent RDP profile that may stimulate microbial growth in the rumen. Although canola meal was extensively degraded in the rumen, its 12-h residue still provided an estimated AA profile to the intestinal tract that was close to the AA profile of milk protein (Piepenbrink and Schingoethe, 1998). Kendall et al. (1991) found that the effective degradability of canola meal averaged 51.5%. This compared to 59.1% for soybean meal. In the current animal feed market in Iran, canola meal is cheaper than soybean meal (320 vs. 482 Toman/kg; US $1=933 Toman). The objective of this experiment was to evaluate substitution of soybean meal with canola meal and measure its effects on milk production and composition, and dry matter intake in early lactation Iranian Holstein cows.