  Flat directions in the minimal supersymmetric standard model are known to
deform into non-topological solitons, Q-balls, which generally possess both
baryon and lepton asymmetries. We investigate how Q-balls evolve if some of the
constituent fields of the flat direction decay into light species. It is found
that the Q-balls takes a new configuration whose energy per charge slightly
increases due to the decay. Specifically, we show that all the stable Q-balls
eventually transform into pure B-balls via the decay into neutrinos.
