We study the decay of a very massive closed superstring (i.e. alpha'M-2 >> 1) in the unique state of maximum angular momentum. This is done in flat ten-dimensional spacetime and in the regime of weak string coupling, where the dominant decay channel is into two states of masses M-1, M-2. We find that the lifetime surprisingly grows with the first power of the mass M: T = calpha' M. We also compute the decay rate for each values of M-1, M-2. We find that, for large M, the dynamics selects only special channels of decay: modulo processes which are exponentially suppressed, for every decay into a state of given mass M-1, the mass M-2 of the other state is uniquely determined.
