We re-conceptualized the meaning of scientific literacy and developed an instrument, which we call the Global Scientific Literacy Questionnaire (GSLQ) based on a new conceptual framework for scientific literacy in the twenty-first century. We identified five dimensions, each with key elements. The five dimensions are (1) content knowledge (core ideas of science), (2) habits of mind (science practices), (3) character and values, (4) science as human endeavor, and (5) metacognition and self-direction. In this study, we attempted to diagnose the extent to which South Korean secondary students perceive themselves as global citizens having such capabilities using GSLQ with 3,202 students (7th-12th grades). Validity and reliability were examined using various statistical techniques including the Cronbach's a coefficient, exploratory factor analysis, and confirmatory factor analysis. The use and value of the instrument were discussed by examining the Korean secondary students' overall scientific literacy as well as their views on each dimension across gender and grade levels. We recommend that teachers and researchers use the GSLQ to assess students' global scientific literacy and provide comments on its usefulness as a research tool and the practical use of its inventory of items.