Objective: To evaluate the antineoplastic activity of Eucalyptus extract (EuE) against Ehrlich ascites carcinoma (EAC) in Swiss albino mice. Methods: Preliminary examination of four plant extracts (namely Eucalyptus, Costus, Azadirachta, Feronia) has been done by observing the reduction ability of number of EAC cells in previously inoculated Swiss albino mice. Among them as EuE showed maximum capability, the whole study has been conducted with EuE only. Important parameters viz. enhancement of life span, reduction of average tumor weight etc. have been studied. In addition the effects of EuE on hematological parameters in both normal and EAC inoculated mice have been measured. Effect of EuE on normal peritoneal cells has also been studied. Results: EuE reduced tumor burden remarkably. It reduced the tumor growth rate and enhanced the life span of EAC bearing mice noticeably. It reversed back the hematological parameters towards normal, reduced the trasplantability of EAC cells and enhanced the immunomodulatory effects in mice. The host toxic effect of EuE in mice is minimum and mostly reversible with time. All such data have been compared with those obtained by running parallel experiments with bleomycin at dose 0.3 mg/kg (i.p.). Conclusions: The Eucalyptus extract may be considered as a potent anticancer agent for advanced researches.