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The precipitation behaviour of beta and gamma' in a low thermal expansion superalloy IN783 was investigated. It was demonstrated that coarse gamma' precipitates do form during beta aging at 845 degrees C. During aging at lower temperatures, not only fine gamma' particles are formed, the coarse gamma' particles also change from spherical to cuboidal. Therefore, a bimodal distribution of gamma' is formed in the matrix after standard aging treatment. The formation of beta consumes Al atoms, which constrains the formation of coarse gamma' in the zone around beta during aging at 845 degrees C. During gamma' aging, a fine gamma' precipitating zone is formed around b. Prolonging the beta aging duration markedly promotes the formation of beta at grain boundaries and in the matrix, significantly enlarges the fine gamma' precipitating zone and influences the precipitation of coarse gamma'.