Juvenile unionid mussels disperse in the water column after detachment from their host fish. The settling velocity (w_s) of juvenile mussels is an important component of their dispersion in the water column but has not been measured for unionid mussels. The goal of our study was to measure the w_s of juvenile mussels in the laboratory and to examine how w_s varied within and among related species. The w_s of Actinonaias ligamentina and Ptychobranchus fasciolaris were significantly lower (2.4 ± 0.1 mm/s vs 2.5 ± 0.1 mm/s, respectively) than those of the larger-sized Lampsilis fasciola and Epioblasma triquetra (4.2 ± 0.2 mm/s vs 4.6 ± 0.2 mm/s, respectively). Overall, w_s increased with juvenile size, but considerable variation (∼10×) was found within species. Observations indicated that foot movement of juvenile mussels was responsible for reductions in w_s, and this behavior may provide a potential mechanism for habitat selection at small-spatial scales. Observed w_s differed considerably from w_s predicted from Stokes' law using empirically determined shell size and density (ρ = 1.22 ± 0.003 g/cm³ for A. ligamentina), which indicates some of the limitations in predicting w_s from size measurements.