  We discuss quantum fluctuations of a class of rotating strings in AdS_5 x
S^5. In particular, we develop a systematic method to compute the one-loop
sigma-model effective actions in closed forms as expansions for large spins. As
examples, we explicitly evaluate the leading terms for the constant radii
strings in the SO(6) sector with two equal spins, the SU(2) sector, and the
SL(2) sector. We also obtain the leading quantum corrections to the space-time
energy for these sectors.
