Abstract Neighborhood walkability, socioeconomic status (SES) and psychosocial factors have each been associated with physical activity. Yet few U.S. studies have examined whether neighborhood SES or individual factors moderate associations between neighborhood walkability and adolescent physical activity levels. Adolescent data (n=1,288) from the NCI Family Life, Activity, Sun and Healthy Eating (FLASHE) study was used. Minutes per day of moderate to vigorous physical activity (MVPA) were calculated using the self-reported Youth Activity Profile and a subsample of participant accelerometer data. Adolescent home address was geocoded and linked to U.S. Census data at varying street network buffer sizes. Neighborhoods were defined by a 400m buffer around each participant's home. Factor analysis of neighborhood population density and built environment features revealed three neighborhood factors associated with walkability: 1) high density and non-auto commutes, 2) older homes, and 3) short auto commutes. Neighborhood SES was measured using the Yost index derived from Census data and categorized into quintiles (1 = lowest SES; 5 = highest SES). Multiple linear regression examined associations between neighborhood walkability factors and adolescent MVPA, and interactions between these factors and 1) neighborhood SES and 2) physical activity self-efficacy. We controlled for age, gender, race/ethnicity, and parent education. Living in neighborhoods with higher density (B=7.3, p=0.003) and older homes (B= 4.7, p=0.007) were positively associated with MVPA. The positive association between living in a higher density neighborhood with more non-auto commutes and MVPA was stronger for those living in neighborhoods at the 2nd and 4th quintiles of neighborhood SES, compared with those in the lowest SES neighborhoods. Similarly, the association between living in a neighborhood with older homes and MVPA was stronger for those living in the 2nd SES quintile compared with the lowest SES. Physical activity self-efficacy was independently positively associated with MVPA (B=18.9, p<.0.001), but did not moderate associations between walkability and MVPA. Neighborhood factors associated with walkability were associated with adolescent MVPA in this national sample of U.S. adolescents. For adolescents living in some higher SES neighborhoods, the association between living in a high-density or older neighborhood and MVPA was strengthened, suggesting that the walkability experience, or types of physical activities engaged in, may potentially vary by neighborhood SES, and are independent of individual self-efficacy. Citation Format: Heather D'Angelo, Laura Dwyer, Linda Nebeling, April Oh. Neighborhood socioeconomic status but not individual self-efficacy moderates associations between neighborhood walkability and adolescent physical activity in the NCI geoFLASHE Study [abstract]. In: Proceedings of the Eleventh AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2018 Nov 2-5; New Orleans, LA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl):Abstract nr C013.