The importance of habitat structure on predation in streams is better understood for mineral substrates than leaf packs. We examined the role leaf pack structure and prey density play on fish (Cottus bairdii) predation of stream invertebrates (Gammarus pseudolimnaeus). We hypothesized that: 1) risk of predation to invertebrates would decrease as habitat structure increased, and 2) predation effects would be proportional to prey density. We also examined whether results were dependent on spatial scale (arena area: 510, 1,225, and 2,331 cm²). We found that the proportion of prey remaining in small arenas increased with leaf pack size (dry mass: 0, 1, 5, and 10 g). The proportion of prey remaining was not influenced by the prey stocking density (15 or 30 individuals/510 cm²), suggesting predation was proportional to prey density. Our results show that leaf packs provide refuge habitats from predation for stream invertebrates and larger leaf packs are better refuge habitats than smaller leaf packs. We also found that our results were not dependent on the size of arenas used. Our research highlights that leaf pack size is an important factor affecting the degree of refuge a leaf pack provides stream invertebrates against fish predation.