Gelatin is an animal-based protein that has been used to improve pellet quality. Previous work with low-bloom gelatin in extruded kibble demonstrated improved hardness and durability but decreased expansion. The objective of this experiment was to clarify the relationship of expansion on product hardness and durability resulting from gelatin inclusion. Two complete diets (30% protein) were produced: a control with no gelatin (OG) and another with 10% low-bloom gelatin (10G) added at the expense of chicken by-product meal. Diets were produced on a Wenger X-20 extruder through a circular die (4.6mm diameter). The extruder screw speed and throttle valve opening were adjusted to achieve 2 densities (HD and LD). Products were analyzed for bulk and piece density, radial expansion, specific length, hardness, and pellet durability index (PDI). Results were summarized with the aid of statistical analysis software (SAS 9.4). Hardness was not affected by treatment (P > 0.05). The main effect means of PDI decreased 33% with the inclusion of gelatin (P < 0.05; 77.57% v 52.25%) and decreased 20% between HD and LD (P < 0.05; 72.17% v 57.65%). The main effect means of radial expansion and specific length increased with gelatin inclusion (P < 0.05; 2.86 v 3.56mm²/mm² expansion and 4.12 v 4.47cm/g length), but were unaffected by HD or LD. The main effect means of piece and bulk density were lower with gelatin inclusion (0.52 v 0.39g/cm³ piece density and 351.8 v 280.7g/L bulk density) and also reduced from HD to LD (0.46 v 0.44 g/cm³ piece density and 345.8 v 266.7g/L bulk density). The means for PDI were affected by the interaction of gelatin level and target density. PDI decreased from HD to LD within the OG diet (P < 0.05; 92.0% v 63.14%) and continued to decrease with the 10G diets. However, there was no difference between HD and LD for the 10G diets (P > 0.05; 52.34% v 52.16% for HD and LD, respectively). The decrease in PDI between 0G and 10G may be due to the increased expansion, but the gelatin may prevent a further decrease in PDI between HD and LD. Low-bloom gelatin may improve the physical properties of high protein pet food without compromising expansion.