  We study the invisible decay of the Higgs boson into a pair of stable, heavy
photons, H -> A_H A_H, in the littlest Higgs model with T-parity. For a
symmetry breaking scale of f = 450 GeV, the branching ratio H -> A_H A_H can be
as high as 93% for Higgs masses below 150 GeV. For f = 500 GeV, the invisible
branching ratio is about 75% in the Higgs mass range 135 - 150 GeV and 10
(5.5)% for m_H = 200 (600) GeV. It drops to a few percent for f larger than 600
GeV. We have found regions in parameter space, allowed by the electroweak
precision data, with such low values of f for 115 GeV < m_H < 650 GeV.
