This paper furthers the study of Adhikari et al. (2010) [2] on the global regularity issue concerning the 2D Boussinesq equations with vertical dissipation and vertical thermal diffusion. It is shown here that the vertical velocity v of any classical solution in the Lebesgue space L q with 2 q < ∞ is bounded by C 1 q for C 1 independent of q. This bound significantly improves the previous exponential bound. In addition, we prove that, if v satisfies T 0 sup q 2 v(·,t) 2 L q q dt < ∞, then the associated solution of the 2D Boussinesq equations preserve its smoothness on [0, T ]. In particular, v L q C 2 √ q implies global regularity.