In this paper, we calculate the next-to-leading-order (NLO) twist-3 contribution to the form factors of B -> pi transitions by employing the k(T) factorization theorem. All the infrared divergences regulated by the logarithms ln(k(iT)(2)) cancel between those from the quark diagrams and from the effective diagrams for the initial B meson wave function and the final pion meson wave function. An infrared finite NLO hard kernel is, therefore, obtained, which confirms the application of the k(T) factorization theorem to the B meson semileptonic decays at the twist-3 level. From our analytical and numerical evaluations, we find that the NLO twist-3 contributions to the form factors integral(+,0)(q(2)) of the B -> pi transition are similar in size but have an opposite sign with the NLO twist-2 contribution, which leads to a large cancellation between these two NLO parts. For the case of integral(+)(0), for example, the 24% NLO twist-2 enhancement to the full LO prediction is largely canceled by the negative (about -17%) NLO twist-3 contribution, leaving a small and stable 7% enhancement to the full LO prediction in the whole range of 0 <= q(2) <= 12 GeV2. At the full NLO level, the perturbative QCD prediction is F-B ->pi (0) = 0.269(-0.050)(+0.054).We also study the possible effects on the perturbative QCD predictions when different sets of the B meson and pion distribution amplitudes are used in the numerical evaluation.