  The one-loop contributions to the branching ratios for leptonic tau decays
are calculated in the CP conserving 2HDM(II). We found that these one-loop
contributions, involving both neutral and charged Higgs bosons, dominate over
the tree-level H^+ exchange, the latter one being totally negligible for the
decay into electron. The analysis is focused on large tanbeta enhanced
contributions to the considered branching ratios. We derive a simple analytical
expression for the one-loop contribution which holds in this case. We show that
the leptonic branching ratios of tau are complementary to the Higgsstrahlung
processes for h(H) and have a large potential on constraining parameters of the
model. In this work we provide upper limits on Yukawa couplings for both light
h and light A scenarios and we derive new lower limit on mass of M_{H^+} as a
function of tanbeta, which differs significantly from what was considered as
standard constraint based on the tree-level H^{+} exchange only. Interestingly
we obtain also an upper limit on M_{H^+}. For a SM-like h scenario, with heavy
and degenerate additional Higgs bosons, one-loop corrections disappear.
