Students in the USA have fallen near the bottom in international competitions and tests in mathematics and science. It is thought that extrinsic factors such as family, community, and schools might be more influential than intrinsic attitudes toward science interest. However, there are relatively few valid and reliable measures of intrinsic factors such as interest relating to science. With the lack of intrinsic measures, it is difficult to determine the impact of extrinsic factors on the intrinsic construct. A fuller picture of the factors affecting intrinsic factors such as science interest will allow interventions to become more refined and targeted. Several studies suggest that student interest toward science affects the likelihood of the student pursuing advanced courses in science. The goal of this paper is to establish the validity and reliability of the Science Interest Survey and to determine if the survey meets the formal requirements of measurements as defined by the Rasch model. Results using both IRT and CRT analysis suggest that Science Interest Survey is an adequate measure of the unidimensional construct known as science interest. Results further suggest the Science Interest Survey is a valid and reliable measure for assessing science interest levels.