  We examine the constraints on non-radiative decay of neutrinos from the
observations of solar neutrino experiments. The standard oscillation hypothesis
among three neutrinos solves the solar and atmospheric neutrino problems. Decay
of a massive neutrino mixed with the electron neutrino results in the depletion
of the solar neutrino flux. We introduce neutrino decay in the oscillation
hypothesis and demand that decay does not spoil the successful explanation of
solar and atmospheric observations. We obtain a lower bound on the ratio of the
lifetime over the mass of $\nu_2$, $(\tau_2/m_2) > 22.7 (\srm/\MeV)$ for the
MSW solution of the solar neutrino problem and $(\tau_2/m_2) > 27.8
(\srm/\MeV)$ for the VO solution (at 99% C.L.).
