The effects of gravity on the growth processes of colloidal crystals were evaluated under low gravity using aircraft flights. Monodispersed colloidal particles, such as polystyrene and silica particles, form colloidal crystals in highly deionized water. Colloidal crystals offer an important opportunity to Study the dynamics of crystallization. The purpose of this study is to observe the gravitational effects on the nucleation and post-nucleation stages of crystal growth in low gravity. The dynamics of colloidal crystallization was evaluated using the in situ optical reflection spectrum method. Although colloidal crystals obeyed the classical nucleation theory under low gravity, on-ground experiments showed an increase of the steady state nucleation rate and a remarkable reduction of the lag time predicted from the classical theory. To confirm the effects of gravitational field, DC electric field was applied based on the consideration that both fields affect the motion of colloidal particles as the directional body forces. The experiments with the electric field under low gravity showed the similar reduction of the lag time under normal gravity. The nucleation mechanism of colloidal crystals under gravity was explained by the enhanced particle adhesion to critical nuclei under the presence of the forced particle and cluster movements.