Cs vapor, mixed with a gas was irradiated in a glass fluorescence cell with pulses of 886nm radiation from a YAG-laser-pumped OPO laser, populating 6D3/2 state by two-photon absorption. Cross sections for 6D3/2→6D5/2 transition induced by collisions with various He atoms and H2 molecules were determined using methods of atomic fluorescence. The resulting fluorescence included a direct component emitted in the decay of the optically excited state and a sensitized component arising from the collisionally populated state. At the different densities, we have measured the relative time-integrated intensities of the components and fitted a three-state rate equation model to obtain the cross sections for 6D3/2→6D5/2transfer: σ=(55±13)×10-16 and (16±4)×10-16 cm2 for H2 and He, respectively. The cross sections for the effective quenching of the 6D5/2 state were also determined. The total transfer rate coefficients from the 6D5/2 state for He is small ［1.2×10-10 cm3·s-1］. The total quenching rate coefficient of the 6D5/2 state is larger for H2［6.7×10-10 cm3·s-1］. For H2 case, the quenching rate coefficient corresponds to reaction and nonreactive energy transfer. Evidence suggests that the nonreactive energy transfer rate coefficient is ［6.3×10-10 cm3·s-1］. Hence the authors estimated the cross section (2.0±0.8)×10-16 cm2 for reactive process Cs(6D5/2)+H2→CsH+H. Using the dependence on the pressure of H2（or He）of the integrated fluorescence monitored at the 6D5/2→6P3/2 transition the cross section (4.0±1.6)×10-16 cm2 for Cs(6D3/2)+H2→CsH+H was obtained. Thus, the relative reactivity with H2 follows an order of Cs(6D3/2)>Cs(6D5/2).