African American (AA) smokers have earlier development of lung disease as well as poorer sleep health than Caucasians. We tested the extent to which sleep health modifies the association between smoking level and functional exercise capacity in a sample of AA smokers.Cross-sectional data from 209 AA smokers (≥1 cigarette in last month) aged 40-65 years with no evidence of sleep disordered breathing (AHI <15) or severe COPD (FEV1>50%), were used for the current study. Self-reported smoking rate, objectively measured sleep efficiency (SE), Total Sleep Time (TST), and the 6-minute walk test (6MWT) for functional exercise capacity were the key assessments.The mean age was 54.8 years (SD=5.96), and mean cigarettes smoked per day (cpd) was 8.71 (SD=6.78). Mean SE was 69.9% (SD=12.3%), and mean TST was 307.99 minutes (SD=92.2). In adjusted linear regression models of the 6MWT (meters), TST (slope estimate= -0.14, p=.14) and SE (slope estimate= -1.0, p=.19) were negatively associated with 6MWT. The smoking rate ⨉ SE interaction was highly significant (slope estimate=0.18, p=.007) such that in individuals who smoked ≥10cpd, every additional % of SE garnered between 0.83 - 6.62 more meters. Similarly, the smoking rate X TST interaction was significant (slope estimate=0.019, p=.03) such that in smokers who smoked ≥10cpd, every additional minute of TST garnered between 0.04 - 0.60 more meters.Higher SE and, to a lesser extent, longer TST, in AA's who smoke ≥10cpd is associated with better 6MWT performance.The study is registered at ClinicalTrials.gov (NCT03534076).