The structural characteristics of oxygen-implanted 6H-SiC, which was annealed at 2650 degrees and 1900 degreesC were studied by Transmission Electron Microscopy (TEM). Oxygen-related clusters are formed during the annealing The size of the clusters increases and their density decreases by increasing the annealing temperature. Tetrahedral precipitates with a mean size of 5nm are developed after annealing at 1900 degreesC for two hours. The precipitates are apparently amorphous suggesting that SiO2 is formed. Significant strain is developed around the precipitates, which imposes a displacement vector R along the c-axis. The large precipitates punch dislocation loops. The loops are always generated at the edges of the precipitates.