The decay rates for light double hypernuclei are estimated and it is noted that the non-mesic decays are of interest. The characteristic decay modes, i. e. Λ-n, Σ--p and Σ0-n decays give us a valuable information on the weak interaction. The relations between the coupling constants of the four-baryon weak interactions are derived from the data for the one-lambda hypernuclei in the framework of the SU(3) symmetry model, and the cancellation of the coupling constants for I = 0 pointed out by Block and Dalitz is compatible with the model.