Several studies have suggested that momentary self-concept clarity (SCC) levels are important for emotion regulation and self-control processes, but these studies have used unvalidated measures of momentary SCC. Here, we report on the development and preliminary validation of a brief self-report scale, the Momentary Self-Concept Clarity Scale (M-SCCS). One hundred and twenty-two adults completed momentary SCC items 6-7 times per day for two weeks. Multilevel factor analyses suggested the M-SCCS has good factorial validity. The scale also showed excellent between-person reliability, fair within-person reliability, and patterns of criterion relations that resemble other self-report measures of SCC. There was little measurement reactivity over time. The M-SCCS may be useful for future experience-sampling studies aimed at uncovering short-term self-regulatory processes involving SCC.