  We show prospects on a search for invisible decays of a Higgs boson at the
Large Hadron Collider (LHC) and High Luminosity LHC (HL-LHC). This search is
performed on a Higgs boson produced in association with a Z boson. We expect
that the branching ratio of 17-22% (6-14%) could be excluded at 95% confidence
level with 300 fb^{-1} (3000 fb^{-1}) of data at sqrt(s)=14 TeV. The range
indicates different assumptions on the control of systematic uncertainties.
Interpretations with Higgs-portal dark matter models are also considered.
