Tunable laser action in the visible spectrum has been established for what is believed to be the first time by use of dye-doped, polymer-silica nanoparticle gain media. The silica nanoparticles, ranging from 9 to 12 nm in diameter, appear to be uniformly dispersed in the poly(methyl methacrylate) matrix because the optical homogeneity of the gain medium is maintained. With Rhodamine 6G dye and 30% weight-by-weight silica nanoparticles, laser action was established in the 567-603-nm range. At the peak wavelength (λ ~ 580 nm), laser conversion efficiency is ~63% at a beam divergence of 1.9 mrad (~1.3 times the diffraction limit). The new solid-state gain medium also exhibits a reduction in |∂n/∂T|.