Many researches have been carried out on production and properties of pre-cast concretes. Currently, most of them have focused on normal concrete, and are unable to completely represent the behavior of lightweight concrete (LWC). In this study, physical and mechanical properties of LWC produced with diatomite and pumice lightweight aggregates after autoclave curing were investigated. In the production of LWC, 0-4 mm maximum sizes of aggregates were used. Cement content and water/cement ratio were kept at 300 kg/m(3) and 0.20, respectively. The specimens were prepared in circle divide 50 x 100 mm cylindrical shape, and after 24 h of demoulding exposed to autoclave curing for 2, 4, 6, 8 and 10 h. Besides, two different cures were applied on the specimens as in water and in air at 20 degrees C +/- 2, respectively. At the end of autoclaving and environmental cure, compressive strength in 7, 28 and 590 d, unit weight, specific porosity, thermal conductivity and water absorption were tested. Also, microstructures of LWC produced with diatomite and pumice aggregate were investigated. As a result, it is concluded that by autoclaving of specimens in 8-10 h, especially, compressive strength of specimens have increased 75% of strength of 28 aged specimens cured in water. (C) 2007 Elsevier Ltd. All rights reserved.