Psychological capital refers to an individual's self-perceived positive psychological state of development. As engineering is always full of challenges and obstacles, it is important to develop the psychological capital of engineering students to make engineering a sustainable career. However, existing instruments are developed in non-engineering contexts. This study selected, modified, and validated an existing instrument to provide accurate measurements for engineering students. The Psychological Capital Questionnaire (PCQ) was modified and validated in two phases. In the first phase, six experts, including chemical engineers, chemical engineering educators, and lecturers in education were recruited for the content validation to review the items. Two items with a content validity index (I-CVI) less than 0.78 were revised based on the suggestions, and the experts revalidated modified items. After the second review round, all items' I-CVI were acceptable. In the second phase, cognitive interviews were carried out with five engineering students. The modified questionnaire was presented to the interviewees to seek their feedback on the clarity of items. Based on students' feedback, items were modified and finalised when no new suggestions were given. Flesch reading ease score was calculated, and it was found that the language in the modified questionnaire could be easily understood. As a research outcome, the modified PCQ is ready to be used among engineering students in the future.