Abstract Background Outdoor air pollution has been reported to be associated with frailty (including slow gait speed) in older adults. However, to date, no literature exists on the association between indoor air pollution (eg, unclean cooking fuel use) and gait speed. Therefore, we aimed to examine the cross-sectional association between unclean cooking fuel use and gait speed in a sample of older adults from 6 low- and middle-income countries (China, Ghana, India, Mexico, Russia, and South Africa). Methods Cross-sectional, nationally representative data from the World Health Organization Study on global AGEing and adult health were analyzed. Unclean cooking fuel use referred to the use of kerosene/paraffin, coal/charcoal, wood, agriculture/crop, animal dung, and shrubs/grass based on self-report. Slow gait speed referred to the slowest quintile based on height, age, and sex-stratified values. Multivariable logistic regression and meta-analysis were done to assess associations. Results Data on 14 585 individuals aged ≥65 years were analyzed (mean [standard deviation] age 72.6 [11.4] years; 45.0% males). Unclean cooking fuel use (vs clean cooking fuel use) was significantly associated with higher odds for slow gait speed (odds ratio = 1.45; 95% confidence interval: 1.14–1.85) based on a meta-analysis using country-wise estimates. The level of between-country heterogeneity was very low (I2 = 0%). Conclusions Unclean cooking fuel use was associated with slower gait speed among older adults. Future studies of longitudinal design are warranted to provide insight into the underlying mechanisms and possible causality.