We study the formation of Q balls which are made of flat directions that ap
pear in the supersymmetric extension of the standard model in the contest o
f gravity-mediated supersymmetry breaking. The full nonlinear calculations
for the dynamics of the complex scalar field are made. Since the scaler pot
ential in this model is flatter than phi(2), we have found that fluctuation
s develop and go nonlinear to form nontopological solitons, Q balls. The si
ze of a Q ball is determined by the most amplified mode, which is completel
y determined by the model parameters. On the other hand, the charge of a ba
lls depends linearly on the initial charge density of the Affleck-Dine (AD)
held. Almost all the charges are absorbed into Q balls, and only a tiny fr
action of the charges is carried by a relic XD field. It may lead to some c
onstraints on the baryogenesis and/or parameters in the particle theory. Th
e peculiarity of gravity mediation is the moving Q balls. This results in c
ollisions between Q balls. It may increase the charge of the Q balls, and c
hange its fate.