Background: Retinyl Palmitate has an important role in the development of organs and essential for various life processes such as cell proliferation and differentiation, vision, reproduction and immune function. Objective: To find out the effect of All-trans-retinyl palmitate on Hematological parameters in Swiss albino mice. Methods: Forty Swiss albino mice were randomly divided into four Groups of 10 animals in each Group and dosed as follows: Group-I, which was a control and given only corn oil (2 ml/kg body weight); Group-II, III and IV were administered All-trans-retinyl palmitate orally 4000 IU/kg body weight/day/mice for four, eight and Twelve weeks of experimental period. Fasting blood samples were collected at the end of 4, 8 weeks and finally at the end of the study i.e.12 weeks for estimation of blood parameters in all 4 Groups. Results: All-trans-retinyl palmitate significantly decreases (P<0.05) all blood parameters ( Hb., TRBC, WBC, PCV, Platelets, blood indices) in the Group-IV as compared to Group-I, II, &III and no significant change (P>0.05) in the Group-II was observed when compared to both control or Group-III. The Prothrombin Time and differential Lymphocyte Count in the Group-IV were significantly higher (P<0.05) when compared to Control, II, III Group and no significant change (P>0.05) was observed in the Group-II as compared to Control and Group-III. Conclusion: It is concluded that All-trans-retinyl palmitate is associated with reduced bone marrow activity in Swiss albino mice. Indexing key words: Hematological parameters, TRBC, WBC, Platelets, Blood indices All-trans-retinyl palmitate