The laser amplification gain of Rhodamine 6G and Rhodamine S was measured by using the second harmonic of ruby laser as exciting light. And the wavelength dependence of gain in various dye conceotrations was experimentally investigated. The reslt clarified that the gain width was the widest near the center of the concentration range for laser oscillation. On the other hand, an amplifiable wevelength renge and wavelength dependence of gain were calculated by substituting the absorption and fluorescence spectra into a formula for determining laser gain. The result of the calculation was confirmed to correspond approximately to the experimental fact.