  The recently proposed trans-Planckian censorship conjecture (TCC) imposes a
strong constraint on the inflationary Hubble scale, of which the upper bound
could be largely relaxed by considering a noninstantaneous reheating history.
In this paper we will show that, if the primordial black holes (PBHs) are
formed at reentry in the radiation-dominated era from the enhanced curvature
perturbations at small scales, the TCC would impose a lower bound on the PBH
mass $M_\mathrm{PBH}>\gamma(H_\mathrm{end}/10^9\,\mathrm{GeV})^2\,M_\odot$
regardless of the details for reheating history, where $\gamma$ is the collapse
efficiency factor and $H_\mathrm{end}$ is the Hubble scale at the end of
inflation. In particular, the current open window for PBHs to make up all the
cold dark matter could be totally ruled out if the inflationary Hubble scale is
larger than 10 TeV. For the case of PBHs formed in an early matter-dominated
era, an upper mass bound is obtained.
