A theoretical investigation has been conducted into the effect of hydrates on the instability of liquid CO2 jets in the deep ocean. It is shown that the effect of hydrates on instability of a liquid CO2 jet depends on the relative magnitudes of the hydrate-formation time, t(f), at which the CO2-seawater interface is covered entirely with hydrates and of the jet-breakup time, t(b), at which the jet breaks up into droplets. If t(b)/t(f) much less than 1, then hydrates cannot form even at a later stage of jet instability and jet breakup is pure hydrodynamic behavior. If t(b)/t(f) similar to 1, then hydrates may form during later stages of jet instability; for this case, droplets produced at the end of the jet may be covered with a thin hydrate layer and these droplets may coagulate to form grape-like hydrate structures if they interact with each other. If t(b)/t(f) much greater than 1, then a thin hydrate layer will form on the surface of the jet at an early stage of jet instability; for this case, a tube-like hydrate structure may occur. The results of this study agree with deep-ocean and laboratory observations reported by previous investigators.