"Mesic decay of hyperfragments is discussed systematically on the basis of a previous model for hyperfragments. The general formalism for the two-body and three-body mesic decay was developed. The polarization-direction correlation and the angular correlation for the two-body and the three-body decays are discussed together with the decay probability. The formalism was developed so as to include the isotopic spin selection rule ( DELTA I = 1/2 and 3/2) for the mesic decays. The theory was applied especially for the low mass number hypergragments where it was found that the branching ratios of the two-body and the three-body mesic decays of /sup 3/H/sub i and /sup 4/H/sub i, (/sup 3/ H/sub i yields /sup 3/He + i/sup -/)/(/sup 3/H/sub i yields D + p+ pi /sup -/) and (/sup 4/H/sub i yields /sup 4/He + pi /sup -/)/(/sup 4/H/ sub i yields /sup 3/H + p + pi /sup -/), could be used for the determination of the spins of both hyperfragments. The fraction of the p-wave decay rate for the free LAMBDA decay obtained from the reaction /sup 5/He/sub i yields /sup 4/He + p + pi where the decay proceeds through two-resonant states (p/sub 3/2/ and p/sub 1/2/) …