The Nature of Scientific Knowledge Scale (NSKS) is a 48 item, Likert-type instrument designed to assess high school students' understanding of the nature of scientific knowledge. This attitude scale is based on a six-factor model adapted from the factor-explication format used by Victor Showalter. Scientific knowledge is characterized as: (1) amoral, i.e., provides people with many capabilities, but does not provide instruction on how to use them; (2) creative, i.e., is a product of human intellect; (3) developmental, i.e., is never "proven" in the absolute and final sense; (4) parsimonious, i.e., tends toward simplicity but not to the exclusion of complexity; (5) testable, i.e., is capable of public empirical test; and (6) unified, i.e., is born out of an effort to understand the unity of nature. When the NSKS was administered to high school and college students, the reliability ranged from .65 to .89. The construct validity of the NSKS was examined by testing an anticipated difference in understanding of the nature of scientific knowledge between two groups of college freshmen with different educational backgrounds. The students who had previously studied philosophy of science had higher mean scores on five of the six NSKS subscales and on the entire NSKS. The scale and instructions for scoring are appended. (MV)