Commiphora swynnertonii is among the most commonly used medicinal plants by pastoralist communities especially in northern regions of Tanzania. The effect of resin from this plant on white blood cells (WBC) and haematopoietic organs was studied using albino mice. Sixty adult mice were randomly assigned into four groups (n = 15). G1 acted as control whereas G2, G3 and G4 received oral doses of 50, 100 and 200 mg resin per kg body weight, respectively for 35 days consecutively. Blood samples for differential and total WBC count were collected before treatment and on days 7, 14, 28 and 35 after treatment. Also, three mice from each group were humanely sacrificed before treatment, on day 14 and 35 after treatment. Sternum, liver and spleen samples from sacrificed mice were collected for assessment of any effects of the resin on haematopoietic organs. Results showed that mice in G2 and G4 had a significant increase (P < 0.05) in total WBC counts by day 7 as compared to the control group. This trend was then followed by a gradual decrease towards end of the experiment. No significant changes in total WBC counts were observed in G3 following treatment. The effect of C. swynnertonii resin on differential WBC count was non-specific and insignificant; G1 and G2 mice had their lymphocyte and monocyte counts slightly increasing with time while that of G3 and G4 decreased slightly or remained unchanged. Neutrophils counts decreased significantly in G1 and G2, but there were no significant changes for G3 and G4. Changes in the haematopoietic tissues following exposure to the resin included increased cellularity of sternal bone marrow as compared to spaces occupied by adipocytes. In particular, there were different developmental stages of granulocytes, erythroblasts and all megakaryocytic series. Small patches of erythropoietic series and lymphoblastic cells were observed in the liver and spleen respectively of the mice that received resin. It is concluded that oral administration of C. swynnertonii resin to mice caused a significant but transient increase in total white cell counts as a short- term effect. Prolonged exposure to the resin was associated with changes in the haematopoietic system such as increased cellularity of bone marrow and erythropoietic patches in liver and spleen.