The effect of transient absorption on a lasing process occurring in a spherical particle was studied by use of a microspectroscopy system combined with a laser trapping technique. Stimulated emission of rhodamine B within a poly (methyl methacrylate) latex particle was greatly attenuated by transient absorption of 9,10-diphenylanthracene simultaneously doped in the particle. Compared with the absorption loss caused by a single path through the particle, the change in the lasing emission intensity was amplified by the optical resonance in a spherical microparticle by two orders of magnitude. The linearity of the emission intensity change with the intracavity transient absorption was also discussed. A new, sensitive method of transient absorption measurement based on the resonance effect is proposed for elucidating picosecond dynamics of a single microparticle.