Psidium guajava (Guava) leaf is used to cure a variety of illnesses, including cough, gastrointestinal pain, gastroenteritis, diarrhea and inflammatory conditions. This study aimed to determine the effect of aqueous extract of Psidium guajava leaf on biochemical and haematological parameters on phenylhydrazine-induced rat. Twenty-Five male Wistar rats, aged between 8 – 10 weeks, were divided into five groups of five rats per group. Group A served as “Normal control”, Group B was induced but not treated, thus served as “Negative control”, Group C was treated with Ferrous (50 mg/kg body weight) while Groups D and E received 300 mg/kg and 600 mg/kg body weight of leaf extract of P. guajava daily, respectively, throughout the duration of the experiment. Anemia was induced via oral administration of 20 mg/kg body weight of phenylhydrazine daily for fourteen consecutive days. Graded doses of the extracts were given by oral gavage once a day for 14 days. The antianaemic effects of P. guajava demonstrated significant increase (P < 0.05) in the hemoglobin (HGB), packed cell volume (PCV) and red blood cell (RBC) count of the extract-treated groups compared to the anemic control group. There was a better increase in the HGB levels of 600 mg/kg (13.50±0.11) compared to anaemic control group (10.13±0.22). The PCV increased more in 600 mg/kg P. guajava (41.00±0.40) compared to anaemic group (26.25±0.85). A significant (P < 0.05) increase was observed in the RBC count of 600 mg/kg P. guajava (5.12±0.05) compared to (3.52±0.23). The outcomes suggest promising therapeutic efficacy of P. guajava extract and ferrous treatments in mitigating anemia-induced hematological alterations.