A laser particle size analyzer was employed to test the grain size of expansive soil, loess, and laterite to examine how sample mass and ultrasonic dispersion time affect the test results. A strong linear positive correlation was observed between shading rate and sample mass. Optimal conditions were determined for the laser particle size analyzer tests: shading rate between 15% and 25%, sample mass of 0.1-0.2 g for expansive soil, 0.4-0.8 g for loess, and 0.2-0.4 g for laterite, with ultrasonic dispersion times of 6 minutes for expansive soil and 2 minutes for loess and laterite. The test results are less discrete for loess and expansive soil but more discretized for laterite. In parallel tests, the maximum range in fraction content for laterite reached 10.1%. Compared to the densimeter method, the laser particle size analyzer reported lower contents of colloidal particles (smaller than 0.002 mm) and higher contents of clay particles (0.005-0.002 mm) or larger fractions. These discrepancies are likely due to the different principles underlying the two methods. The substantial differences in test results for laterite may be attributed to its unique properties. This study provides valuable insights for utilizing laser particle size analyzers in the grain-size analysis of special soils.