We investigate the nonleptonic decays of Ω on the basis of the relativistic composite model. The amplitude of Ω → ΛK^- is dominated by Ξ^0-pole and shown to be consistent with the calculated one in this model. The penguin interaction gives a small correction for this process, but plays an essential role in Ω → Ξπ decay through K-pole contribution. The last situation is quite different from that of the ΔI = 1/2 rule in hyperon decay, where the one-baryon transition governed by the Miura-Minamikawa theorem plays an important role. The observed ΔI = 3/2 parts in Ξπ decay modes and also in the hyperon decays are reduced to the contribution from the quark-decay process.