In the pelleting process, mash feed passes through a conditioner were it is exposed to steam under high pressure and pushed through the die to form pellets. To determine the effect of adding different amounts of water and different thermal processing parameters on the pellet conversion percentage, pellet durability index (PDI) and solubility of protein in KOH of broiler feed. The processing factors were combined in a 4x2 factorial scheme: four moisture addition levels (0%; 0.7%; 1.4%; 2.1%), and two thermal processes (conditioning-pelleting or conditioning-expanding-pelleting). Eight samples of each treatment were collected to evaluate quality parameters. The feed used in this study was a typical corn-soybean broiler diet processed in a commercial feed mill. The pellet conversion percentage and PDI responded linearly and positively in the range of 0 to 2.1% moisture addition. Positive and linear equations relating moisture addition in the conditioner with pellet conversion percentage and PDI were obtained (p<0.001). Expansion improved PDI and pellet percentage respectively by 18% and 21% when compared to simple conditioning-pelleting feed processing. However, an adverse effect on protein quality was observed when higher processing temperature was used. No particle size effect was observed for conditioned-expanded-pelleted feed. Medium particle size resulted in better PDI and higher pellet conversion percentage (p < 0.001) compared to coarse grinding (% pellets – 66.97% versus 64.96%; PDI – 77.30% versus 66.10%).