The effects of formulating broiler diets that contain sources of either rapidly or slowly digestible protein and 2 different dietary fiber sources on growth performance were studied in broilers chickens from 0 to 36 d of age. A total of 1,920 one-day-old, male Ross 708 broiler chickens were randomly allocated and housed in 48 floor pens (40 birds/pen) to one of 4 dietary treatments. Birds were allotted according to a completely randomized block design using a factorial arrangement of treatments with 2 protein digestion rates (rapidly or slowly) and 2 dietary fiber sources [3% oat hulls (OH) or 3% sugar beet pulp (SBP)] from 0 to 36 d of age. All diets were formulated to be isocaloric and isonitrogenous. The pen was the experimental unit for all variables studied (12 replicates/treatment). Data were analyzed using the MIXED procedure of SAS, and the model included the main effects of the protein digestion rate, dietary fiber source, and their interaction. There were 3 experimental feeding phases; starter (from day 0-14), grower (from day 14-28), and finisher (from day 28-36). Results indicated that broilers fed diets containing sources that supplied more rapidly digestible protein had 4% greater (P < 0.01) ADG and improved (P < 0.01) the feed conversion ratio (FCR) by 5% throughout the experiment, most notably after the starter phase. Diets containing 3% OH increased (P < 0.05) the ADFI and ADG (P < 0.05) in the starter phase compared with broilers fed diets containing 3% SBP, without affecting the FCR. The ADG and FCR of broilers fed diets containing sources of slowly digestible protein were improved (P < 0.05) to the level of broilers fed rapidly digestible protein containing diets with the addition of 3% OH. It is concluded that broiler diets should be formulated to contain a high concentration of ingredients that supply rapidly digestible protein, but if this is cost-prohibitive, then 3% OH could be used to increase the ADFI and ADG and potentially protein digestion rates to reduce the FCR.