Summary: This paper presents the results of a laboratory study to evaluate the effect of rubber gradation and content, air voids, aggregate gradation, mix, temperature, and curing conditions on the properties of rubber modified asphalt mixtures. Twenty different mix combinations were evaluated for diametral modulus and fatigue at two different temperatures (-6°C, +10°C). This paper presents only the results of the tests at +10°C. The findings of this study indicate that the rubber gradation and content, aggregate gradation, and use of surcharge during sample preparation have considerable effect on the design asphalt content and on the modulus and fatigue life of the mix. This laboratory data were used to develop guidelines for use of rubber asphalt mixes in Alaska.