Quantum corrections to the conductivity due to the weak antilocalization (WAL) and electron–electron interaction (EEI) effects are investigated in Sb–Te layers to evaluate the number of independent conduction channels in the topological insulator system. We separate the two contributions in the logarithmic temperature dependence of conductivity relying on their distinct response to a magnetic field. For the WAL effect, the amplitude parameter α being− 1 observed in magnetoconductivity is confirmed. The magnitude of the EEI contribution is too large to be produced by one transport channel. The mixing between the surface and bulk states is thus indicated to be weak in the Sb–Te system. In addition, the disorder scattering appears to be less influential for the EEI effect than for the WAL effect.