This study aimed to elucidate the protective role of fennel oil on in hepatic tissue, restoration of total protein and glycogen content formaldehyde induced hepatotoxicity in male rabbits by histological, histochemical, immunohistochemical and biochemical investigations . Twenty-four rabbits were divided into 4 groups (6 rabbits each).  G1:  This group was served as normal controls, G2: This group was administrated with fennel oil (0.3 mg/kg / ip ) for 14 days . G3: this group was administrated with formaldehyde (10mg/kg/ip ) for 14 days. G4: This group administrated with fennel oil then after 3 hours was injected with formaldehyde. In comparison with control group, histological results showed that formaldehyde induced many histopathological alterations as leucocytic infiltration, blood venues congestion, proliferation of bile duct and hemorrhage. Histochemical demonstrations showed that formaldehyde induced marked depletion in   both hepatic total proteins and glycogen contents. PCNA-positive stained nuclei were significantly increased in formaldehyde – treated group. Biochemical investigations of serum liver function markers indicate that; formaldehyde induced significant elevation of AST, ALT, ALP and bilirubin; while albumin level was decreased. Co-treatment of fennel oil and formaldehyde induced a marked degree of improvement and marked decrease of PCNA-positive stained nuclei. Moreover, serum levels of ALT, AST, ALP and bilirubin were significantly decreased, and albumin level was increased.