Purpose: To develop an instrument that measures seogeulpeum in Korean middle-aged adults. Design: An extensive literature review, examination of existing instruments, and three focus group interviews revealed three domains of seogeulpeum: physical characteristics, psychological characteristics, and social characteristics. An original 42-item questionnaire was drafted. Five experts examined its content validity and reduced it to 32 items. To refine the instrument further, and test its reliability and validity, data were collected from 521 middle-aged participants in Korea. Results: Principal component factor analysis of the instrument using varimax rotation indicated that seven factors explained 52.12% of the total variance. Discussion and conclusions: This instrument demonstrated high reliability and validity; therefore, it is an appropriate measure of seogeulpeum for Korean middle-aged adults. Implications for practice: How seogeulpeum differs from depression and grief, if it can develop into a disorder, and how it should be treated require further examination.