  We study the stability of branonium. Contrary to the previous arguments,
global structure of branonium is not stable against spatial fluctuations. We
show that branonium decays into local objects, which looks like Q-balls in the
effective action. Therefore, we consider the idea of brane Q-balls in this
paper. Brane Q-balls are produced as the remnants of unstable branonium.
Although the brane Q-balls are conceptually different from the conventional
Q-balls, they look similar in some parametric regions. We show how to
distinguish brane Q-balls from conventional Q-balls.
