This study aimed to develop and validate a scale of parental competency of science-gifted students in South Korea. The parental competency of science-gifted students is constructed in three dimensions (Learner, Fosterer, Scientist) from the literature review. We in-depth-interviewed science-gifted students and parents to discover the competency behavior indicators. To confirm the content validity, 15 experts in Korea conducted a Delphi method. We were determined lifelong learning, information utilization as the sub-elements of learner, partnership, parenting attitude, empathy of fosterer, and science capability, responsibility in science, and career preparation of scientist. As a result, we developed the initial instrument with 45 items. To validate the instrument, we carried out an online survey with 512 parents. Finally, 23 items of the measurement instrument for parental competency underwent development with three dimensions and eight sub-dimensions. This study provides a reliable instrument for parental competency and contributes to its enhancement for science-gifted students.