We present the first search for gravitational waves from the coalescence of stellar mass and subsolar mass black holes with masses between 20-100 M⊙ and 0.01-1 M⊙(10-103 MJ), respectively. The observation of a single subsolar mass black hole would establish the existence of primordial black holes and a possible component of dark matter. We search the ∼164 day of public LIGO data from 2015-2017 when LIGO-Hanford and LIGO-Livingston were simultaneously observing. We find no significant candidate gravitational-wave signals. Using this nondetection, we place a 90% upper limit on the rate of 30-0.01 M⊙ and 30-0.1 M⊙ mergers at <1.2×106 and <1.6×104 Gpc-3 yr-1, respectively. If we consider binary formation through direct gravitational-wave braking, this kind of merger would be exceedingly rare if only the lighter black hole were primordial in origin (<10-4 Gpc-3 yr-1). If both black holes are primordial in origin, we constrain the contribution of 1(0.1)M⊙ black holes to dark matter to <0.3(3)%. © 2021 authors.