Nanoparticles (NPs) not only offer a great possibility for biomedical application, pharmaceutics, but also may be used for novel diagnostic and therapeutic approaches. Currently, there are no data available regarding to what extent the degree of toxicity of gold nanoparticles (AuNSs). This study aimed to investigate the histopathological and ultrastructural effect of AuNSs size on the liver and kidney of female pregnant rats. To achieve that gold nanoparticles of 10 nm, 25nm and 50 nm were Interperitoneally injected in female rats at 48 hr during rat pregnancy. Forty adult female albino rats were divided into four equal groups: The first one served as a control group, the second received 75 mg/kg/day AuNSs as 10 nm in size, the third received 75 mg/kg/day AuNSs as 25 nm in size and the fourth received 75 mg/kg/day AuNSs as 50 nm in size, All groups were scarified after 19days from gestation where liver and kidney specimens were collected at the end of the experiment for histological and ultrastructural examination, AuNSs treated groups revealed wide spread histological and ultrastructural alterations in the liver and kidney structure as dilated and congested hepatic blood vessels, widespread vacuolated and ballooned hepatocytes with early apoptotic changes, pyknotic hyper chromatic irregular nuclei with deteriorated chromatin condensation. The distal convoluted tubule had shrunken pyknotic nuclei and margination of heterochromatin with irregular nuclear envelope. This study conculcated that all size of AuNSs caused side effect in the liver and kidney of pregnant rates.