  We study the light-element abundances in supersymmetric model where the
right-handed sneutrino is the lightest superparticle (LSP), assuming that the
neutrino masses are purely Dirac-type. In such a scenario, the lightest
superparticle in the minimal supersymmetric standard model sector (which we
call MSSM-LSP) becomes long-lived, and thermal relic MSSM-LSP may decay after
the big-bang nucleosynthesis starts. We calculate the light-element abundances
including non-standard nuclear reactions induced by the MSSM-LSP decay, and
derive constraints on the scenario of right-handed sneutrino LSP.
