  The achievable tanbeta determination accuracy for CMS at LHC is presented.
Using MSSM H/A->tau tau decay in the associated production process gg->bbH/A
the event rates are measured at large tanbeta and the systematic and
statistical errors are estimated. Due to sensitivity of the above event rates
to tanbeta it is shown that it is possible to determine constraints on tanbeta
for a given set of SUSY parameters and uncertainties.
