A finite-size test was carried out for the finite-temperature chiral phase transition in QCD for flavor number Nf=4 and 2 on a lattice with four time slices using the Kogut-Susskind quark action at quark mass of 0.025 in lattice units. All the evidence supports a first-order transition for Nf=4. For Nf=2, however, the data on spatial lattice up to 123 fail to yield convincing finite-size signatures for a first-order transition at this quark mass.