Plant extracts have been found to be very useful for purposes of treatment of diseases among other benefits. Aloe vera is one of such plants whose histological and haemopoietic effect on albino wistar rats were studied. Thirty (30) male wistar rats weighing 140-180g were used for the study. Results showed that extract of Aloe vera had negative effect in the haemopoietic system. The extract reduced the haemoglobin concentration, packed cell volume, white blood cell count and platelet count in test rats (P<0.05). There was increase in the percentage neutrophils. The histological result of the liver cells showed distortions of the liver cyto architecture. It could be deduced from this study that Aloe vera extracts contains some principles that is not favourable to the haemopoietic system and liver cells.