To maximize the contributions of nanotechnology to this society, at least 60 countries have put efforts into this field. In Taiwan, a government-funded K-12 Nanotechnology Programme was established to train K-12 teachers with adequate nanotechnology literacy to foster the next generation of Taiwanese people with sufficient knowledge in nanotechnology. In the present study, the Nanotechnology Attitude Scale for K-12 teachers (NAS-T) was developed to assess K-12 teachers' attitudes toward nanotechnology. The NAS-T included 23 Likert-scale items that can be grouped into three components: importance of nanotechnology, affective tendencies in science teaching, and behavioural tendencies to teach nanotechnology. A sample of 233 K-12 teachers who have participated in the K-12 Nanotechnology Programme was included in the present study to investigate the psychometric properties of the NAS-T. The exploratory factor analysis of this teacher sample suggested that the NAS-T was a three-factor model that explained 64.11% of the total variances. This model was also confirmed by the confirmatory factor analysis to validate the factor structure of the NAS-T. The Cronbach's alpha values of three NAS-T subscales ranged from 0.89 to 0.95. Moderate to strong correlations among teachers' NAS-T domain scores, self-perception of own nanoscience knowledge, and their science-teaching efficacy demonstrated good convergent validity of the NAS-T. As a whole, psychometric properties of the NAS-T indicated that this instrument is an effective instrument for assessing K-12 teachers' attitudes toward nanotechnology. The NAS-T will serve as a valuable tool to evaluate teachers' attitude changes after participating in the K-12 Nanotechnology Programme. (Contains 4 tables, 2 figures and 2 notes.)