In situ developments of platelike spodumene–diopside grains were obtained by controlled devitrification of the complex system Li2O–CaO–MgO–Al2O3–SiO2 glass. The crystallization mechanisms of spodumene–diopside glass were measured by isothermal and non-isothermal processes using classical and differential thermal analysis techniques. The Avrami constant n was 2.0–2.1, indicating two-dimensional crystal growth and platelike grains. The crystalline phases precipitated first were high-quartzs.s., then transformed to β-spodumene and diopside. The Flexural strength, fracture toughness and thermal shock resistance (in 20°C water) increased from 145 MPa, 1.3 MPa m1/2, 800°C (pure spodumene) to 197 MPa, 2.9 MPa m1/2 and 920°C (spodumene–diopside) with low thermal expansion coefficient (from 3∼9·10–7 to 11.8·10–7 K–1). This mean in situ developments of platelike spodumene–diopside grains reinforced the low thermal expansion coefficient glass-ceramics.