Teachers' Internet self-efficacy plays a critical role in their web-based professional development and on their students' learning outcomes in Internet-based learning environments. It is therefore important to periodically measure and evaluate teachers' self-efficacy regarding the Internet, which is a dynamic technology, using an instrument that reflects the recent advancements in the Internet technology. By considering radical changes taking place recently on the Internet, this study aimed to explore teachers' Internet self-efficacy by gender by adapting an earlier instrument. To this end, the Internet Self-efficacy Scale (ISS) developed by Kim and Glassman (2013) was used. First, the ISS was adapted into Turkish and the confirmatory factor analysis results revealed that the Turkish version of the ISS could be used as a valid instrument to measure teachers' Internet self-efficacy [?[superscript 2](df = 106) = 270.836, NFI = 0.865, CFI = 0.912 and RMSEA = 0.086 (90% C.I.; 0.073 - 0.098)]. The coefficient of Cronbach's alpha for the Turkish version of the ISS was found to be 0.92. In this study, survey method was used. The sample of the study consisted of 349 in-service teachers with different majors in Turkey. The data were analyzed using independent sample t-test and the results showed teachers' Internet self-efficacy was considerably high. Additionally, no gender differences in any of the subscales of the ISS including five subscales, namely, reactive/generative, differentiation, organization, communication and search, were found.