The choices of experimental design as well as of statistical analysis are of huge importance in field experiments. The efficiency of alpha lattice design and randomized complete block design (RCBD) were compared in maize trials conducted in 2010 at Bako Agricultural Research Centre (BARC), in Ethiopia on 45 treatments to assess the efficiency of each in minimizing experimental error, coefficient of variation and error mean square for yield variable. The coefficient of variations (CV) compared to be 12.6 % for alpha lattice design and 14.6 % for RCBD respectively. The value of relative efficiency 1.35 indicates that the use of alpha lattice design instead of RCBD increased experimental precision by 35 percent. The gain is considerable in terms of efficiency attained by using alpha lattice design which favors wider use of these designs under field conditions. Based on the results we conclude that alpha lattice designs are more efficient than RCBD. In order to increase the precision of agricultural field experiments researchers are advised to use alpha lattice designs for large number of treatments compared to RCBD.