The sustainability motive-alignment hypothesis posits that adolescents will be motivated to act sustainably when they view sustainable behavior as aligned with their motives for autonomy and peer status. Based on this hypothesis, we developed the Sustainability Motive-Alignment Scale (SMAS), a brief self-report scale of individual differences in sustainability motive-alignment. In four studies across two relatively individualistic (U.S., Netherlands) and two relatively collectivistic countries (China, Colombia), the SMAS was reliable and valid as a single-factor scale; measurement invariant in terms of age and genders but measurement noninvariant in terms of culture, suggesting cultural differences in adolescents' construals of sustainability motive-alignment; and positively associated with measures of sustainable attitudes, norms, self-efficacy, behavior, and climate change knowledge. Thus, sustainability motive-alignment can be assessed as a conceptually distinct psychological dimension underlying adolescents' sustainable tendencies. We hope that our brief, psychometrically sound instrument will spark developmentally informed research on the psychological underpinnings of adolescent sustainability.