The present paper describes the results of the experimental and theoretical investigations made on the bearing capacity of lightweight aggregate concrete. Laboratory tests were conducted to clarify the effects of the dimension of the specimen, the ratio of footing area to loading area of the specimen and concrete mix proportion on the bearing capacity of the cylindrical concrete specimen, which was loaded to be subjected to circular pressure at the center of the top and supported by the entire surface at the bottom. The similar loading tests were also carried out on normal concrete. From this test, the following conclusions were obtained:(1) The bearing capacity (σu) was nearly proportional to compressive strength (σc) ranging from 200 to 400kg/cm2 for normal concrete, but σu was not proportional to σc for lightweight concrete. The ratio of the bearing capacity of lightweight concrete to that of normal concrete were about 1.0, 0.85 and 0.70 when the compressive strength was about 200, 300 and 400kg/cm2, respectively.(2) It is found, therefore, that the coefficients included in conventional empirical formulas to determine the bearing capacity of lightweight concrete should be varied in accordance with the change of concrete strength.(3) The results showed that there was no obvious difference due to the influencing factors, except concrete strength, between the normal and the lightweight aggregate concrete. Moreover, the characteristics of the approximate theoretical solution derived by the author were disccused and compared with the test results obtained and the solutions proposed by other researchers.