We report on anomalous small-angle X-ray scattering (ASAXS) investigations of the formation and structure of nanosized ZrTiO4 crystals in lithium-alumino-silicate (LAS) glass during heat treatment at 750 °C for different periods of time. For a sample annealed for 30 min, ASAXS measurements near the X-ray absorption edge of Ti and Zr reveal the formation of particles (ZrTiO4) surrounded by a shell-like region. The sample annealed for 240 min shows the formation of two different types of particles (spherical core-shell: ZrTiO4 and large spherical particles: LiAlSi 2O6). Additionally, ASAXS results allow quantitative determination of the average composition and volume fraction of the nanocrystals, the surrounding region (shell), and the remaining glass matrix. Data analysis reveals the formation of an alumina enriched region around ZrTiO4. This alumina enriched layer makes the glass network rigid and hinders further growth of ZrTiO4 nanoparticles. For a prolonged annealing time (240 min), a new phase (LiAlSi2O6) is formed additionally, and the (Al/Si) ratio in the shell surrounding the ZrTiO4 crystals decreases. Moreover, the unannealed sample also shows the formation of a Ti enriched phase during cooling of the samples. The obtained quantitative information helps to understand the crystallization and growth mechanisms of ZrTiO4 nanocrystals in LAS glass ceramics.