The Rb(5DJ)+H2→RbH［X １Σ＋(ｖ″＝０)］+H photochemical reaction was studied in a cell experiment applying a laser pump-absorption technique. Using two-photon excitation of the Rb5 2D atomic level in a Rb-H2 vapor mixture, the resulting fluorescence includes a direct component arising from the optically excited state and a sensitized component due to the collisionally populated fine-structure state. The RbH molecules are formed in three-body reactive collisions between excited Rb5 2D atoms and ground state H2 molecules. Near-infrared absorption band RbH X 1Σ＋(v″＝０→ｖ′＝17) near 852 nm by using a diode laser was measured. The absorbed intensity of laser beam through a length L of the RbH vapor is defined as ΔΙ′ and ΔＩ″ where ΔＩ′ and ΔＩ″ are the absorbed intensity of pumping 5D3/2 and 5D5/2 levels, respectively. The ratio of ΔＩ′ to ΔＩ″ contains information on reactivity. ｗ５Ｄ３／２ and w５Ｄ３／２ are the production rates of Rb in the 5D5/2 and 5D3/2 levels by direct laser excitation from the 5S1/2 level. Using a second experiment in which pump laser is used to pump the 5D3/2 and 5D5/2 states in a pure Rb vapor (T=290 K), and the i′/i″ where ｉ′ and ｉ″ are measured intensities of the 5D3/2→5P1/2 and 5D5/2→5P3/2 transition, respectively, is determinined. At low density of Rb atoms, the 5D mixing rate is neglect. The rate of 5D3/2 and 5D5/2 fluorescence yields the ratio of 5D3/2 to 5D5/2 pump production rate. The rate equations were solved, and the authors estimate the value of the cross section at T=385 K and ＰＨ２＝400 Pa for collisional energy transfer from Rb5D3/2 to 5D5/2, from Rb(5D)to Rb states other than Rb(5D)to be 9.8×10-16 cm2 and 2.0×10-16 cm2, respectively. The reaction cross sections ［i.e., Rb(5DJ)+H2→RbH+H］ for J being 3/2 and 5/2 are 5.4×10-17 and 2.3×10-17 cm2, respectively. The relative reactivity with H2 for two studied atoms is in an order of Rb(5D3/2)＞Rb(5D5/2), and this is consistent with the result obtained from a laser pump-probe technique.