The as-cast, heat-treated and long-term aged microstructures of DD6 single crystal superalloy blades with low angle boundaries (LABs) were investigated with scanning electron microscope (SEM) and transition electron microscope (TEM). The coarse γ′ phase and bulk γ/γ′ eutectic precipitate along LABs in the as-cast microstructure. There is a thin layer of γ phase in the grain boundaries and imperfect cubic γ′ particle along grain boundaries in the microstructures after heat treatment. The granular carbide exists, but no TCP phase precipitates along grain boundaries after aging at 1070 oC for 500 h, and LABs of DD6 alloy exhibit good microstructure stability.