The purpose of this study was to develop, validate, and establish the reliability of an instrument that measures preservice teachers' self-efficacy in regard to the teaching of science as inquiry. The instrument, Teaching Science as Inquiry (TSI), is based upon the work of Bandura (1977, 1981, 1982, 1986, 1989, 1995, 1997), Riggs (1988), and Enochs and Riggs (1990). Self-efficacy in regard to the teaching of science as inquiry was measured through the use of a 69-item Likert-type scale instrument designed by the author of the study. Based on the standardized development processes used and the associated evidence, the TSI appears to be a content and construct valid instrument with high internal reliability for use with preservice elementary teachers to assess self-efficacy beliefs in regard to the teaching of science as inquiry.