Abstract: The aim of this study is to investigate the effect of dietary nutritional value (protein source and amount) and temperature on shell morphology of cultured abalone juveniles. Morphological variations have long been used by ecologists and evolutionary biologists to identify physiological and/or environmental conditions associated with the growth and health of organisms. Two important factors affecting morphological plasticity are food supply and temperature conditions. Two different experiments were conducted to test the effect of dietary protein (source and amount) and water temperature on shell morphology (length, width, height, thickness and weight) of juvenile abalone (Haliotis iris). In the first experiment, nine different dietary protein sources (white fish and red fish meals, blood meal, meat and bone meal, casein, soybean concentrate, wheat gluten, maize gluten and Spirulina powder) resulted in wider, higher and heavier shells with casein diets and flatter shells with red fish meal. Abalone fed blood meal produced significantly narrower, thinner and lighter shells compared to animals fed the other diets. In the second experiment, six different dietary protein amounts (0, 10, 20, 30, 40 and 45%) and two temperature regimes (13-21 and 8-16°C) resulted in wider and heavier shells with increasing protein content. However, shell height and thickness were not affected by different protein amounts. Significant differences between temperatures were observed only for shell height and thickness. The results suggest that diet and temperature may be used to manipulate abalone shell morphology in aquaculture environments and they may be potential factors in shell variations of wild populations.