We present the first experimental study of the exciton spin relaxation dyna
mics in InGaN/GaN multiple quantum well structures after quasi-resonant pic
osecond excitation with linearly polarized light. Whereas short spin-relaxa
tion times are generally expected in GaN-based bulk structures, for multipl
e quantum well structures we found long spin-relaxation times, around 100 p
s, when the indium content was not too high. Our results suggest that the e
nergy relaxation toward the radiative state can preserve the linear polariz
ation of the exciton.