7 The material of choice for space applications which demand very high dimensional stability is lithium aluminosilicate (LAS) based Ultra Low thermal Expansion Glass-Ceramic (ULEGC). Generally, the controlled crystallization process recommended for the processing of transparent ULEGC involves a long soaking duration to achieve the required crystal number density. This paper brings out the process optimization procedure adopted for realizing transparent and nanocrystalline ULEGC from conventionally processed LAS glass using microwave-assisted (hybrid) crystallization. The experimental strategy involves two stages (i) identification of the optimum crystallization temperature (T-c) under a microwave field (ii) optimization of a microwave-assisted crystallization process to achieve near zero Coefficient of Thermal Expansion (CTE).. Optimum heat-treatment schedules for nucleation and crystallization under a microwave environment were found to be 720 degrees C/24hours and 775 degrees C/0.3hours, respectively. The optimized heat-treatment condition revealed the efficacy of the microwave hybrid heating, by producing nanocrystalline (35-50nm) and transparent (>82%) ULEGC having a thermal expansion of -0.03 x 10(-6) K (0 degrees C to 50 degrees C).