The present study was conducted to determine the effects of grain (barley vs. corn) and protein sources (soybean meal (SBM) and Corn Gluten Meal (CGM)) on diet selection, milk yield and milk compositions of choice-fed Goats. A 2 by 2 factorial design was employed with 2 grain sources (barley or corn) and 2 protein sources (soybean meal; SBM or Corn Gluten Meal; CGM) as main effects. The groups received grain and protein sources besides wheat bran and alfalfa hay, which chopped in 1.5-2 cm length. Each group received feed stuff as free choice ad libitum in a special trough divided into 4 parts for grain and protein sources, wheat bran and alfalfa hay for a week training + an 8-weeks testing period. The results showed that type of grain (barley or corn) and protein (SBM or CGM) affected the nutrient contents of diets selected. The does offered barley as a grain source consumed higher amount of protein sources. The does offered SBM as protein source selected the diet having lower ADF, NDF and RUP contents and higher CP content than those offered CGM as a protein source. Grain x protein source interaction also affected (p<0.05) nutrient composition of the diets selected. In barley groups, the does offered CGM selected diets with higher NDF but lower ME content than those selected by the does offered SBM, however, no such a difference according to the protein source was observed in the groups receiving corn. Live weight change, dry matter intake (DMI), DMI/milk yield ratio and ME intake were lower (p<0.05) in the groups receiving barley than those having corn. Fat corrected milk yield, fat and protein yield and ADF intake were higher (p<0.05) for the does offered CGM than those offered SBM. ADF and NDF intakes and milk NPN contents were affected (p<0.05) by grain x protein source interaction. The does receiving SBM with barley consumed less ADF and NDF than the does receiving CGM with barley, but the does offered corn did not change their ADF and NDF intakes according to the protein sources. Milk NPN content was decreased by CGM with barley. The results suggest that lactating goats have a good nutritional wisdom that allowing them to select nutritionally balanced diet and to avoid feedstuffs causing nutritional discomfort when different grain and protein sources were supplied simultaneously and freely.