The elastic properties, molar volume, and glass transition temperature (Tg) of rare‐earth‐containing aluminosilicate glasses were investigated in the compositions of SiO2–LnAlO3and SiO2–Ln3/4Al5/4O3, where Ln is Y, La, Nd, Eu, or Yb. The molar volume decreased with decreased ionic size of the Ln3+ion, andTgand elastic moduli increased in the same order. The Yb‐containing glasses showed the highest Young's modulus among all the oxide glasses, even higher than the highest value ever known for glass containing Y2O3, as expected from the smaller ionic radius of Yb3+than that of Y3+. The bulk modulus was found to be almost proportional to the inverse four‐thirds power of the molar volume of glasses in each composition, indicating that Ln3+ions can substitute for each other without changing the glass structure except for the size of the local structure around themselves. From the comparison of these properties, the structural role of rare‐earth ions in these glasses