Abstract: Effects of solid solution temperature and holding time on microstructure and mechanical properties of HR3C austenitic heat resistant steels in solid solution state and in aged state were investigated, respectively. The results show that the grain size changed slightly when solid solution temperature was at 1 150-1 200 ℃, and the grains grew up obviously when solid temperature was above 1 200 ℃. Holding time had a little influence on grain size. With the increase of solid solution temperature and holding time, both size and amount of prime precipitated phases decreased. M23C6 phase precipitated along grain boundaries during the aging at 700 ℃, and grew up with the increase of aging time and coarsened obviously after aging for more than 1 000 h. The fine and dispersed Z phase precipitated in grains and its size was less than 100 nm. With the increase of aging time, the size of Z phase remained unchanged, while its amount increased continuously. The fine and dispersed Z phase played a precipitation strength role in the steel after aged at high temperature for a long time. With the prime solid solution temperature increasing and holding time prolonging, the corresponding elevated temperature yield strength of the aged steel was improved obviously.