Nozzle is one crucial part of rocket. In this research, the nozzle was made by AISI 4340 coated by termal barrier coating (TBC). The TBC material is Al2O3-SiO2 composite, with different variation: Al2O3 - 20% SiO2; 70% Al2O3 - 30% SiO2; and 60% Al2O3 - 40% SiO2. The aim of this research to observe the composittion which will produce optimum adhesive strength and the most widely formed mullite phase. Mullite is an expected phase formed from composite and it has thermal resistance during 1300°C. Coating process was conducted by flame spray with variation of plies. The effect ratio, plies, microstructure, phase, and adhesive strength of TBC were investigated using Scanning Electron Microscope (SEM), X-ray diffraction (XRD),) and adhesion testing. The results showed that the highest adhesive strength was 16 MPa for 20%SiO2 with 2 plies. The highest mullite forming was TBC. After heat treatment, it was found that the mullite phases were most widely formed at a composition of TBC 30% SiO2-70% Al2O3.