  We consider effects of the isocurvature perturbation in the framework of the
tracker-type quintessence models. During the inflation, fluctuations in the
amplitude of the quintessence field are generated, which provide isocurvature
component of the cosmic density perturbation. Contrary to the conventional
notion, it is shown that effects of the isocurvature fluctuation may become
sizable in some cases, and in particular, the cosmic microwave background
angular power spectrum may be significantly enhanced due to the effect of the
isocurvature mode. Such an enhancement may be detectable in on-going and future
experiments.
