Background: Mercury (Hg) is a toxic heavy metal that has been recognized as one of the strongest environmental pollutants. Exposure to Hg even in low doses can induce adverse effects on the structure and functions of the different body organs including gonads.  Celery (Apium graveolens) leaves are rich with antioxidant compounds like apiin, apigenin, and quercetin, and vitamins like E and C. Aim: This work aimed to evaluate the possible modulatory role of celery leaves extract against gonadal toxicity induced by HgCl₂ in female rats and their pups during gestation and lactation periods. Material &methods: Twenty-four female Wistar rats (180-200g) were used in this experiment.  They were mated with males. After confirmation of the gestation test, the pregnant rats were divided into four groups (six for each) as follows: control, celery extract (CE) supplement (200 mg/kg b.wt), HgCl₂ (2mg/kg b.wt) and HgCl₂ co-supplemented with CE groups. The experiment extended from the 4^th day of gestation till the end of the weaning period. At the end of weaning, the female rats and their pups were weighed and sacrificed to collect the blood and remove the gonads for estimation of biochemical and histopathological changes. Results: The obtained results revealed that exposure of female rats to HgCl₂ resulted in a significant decrease in the activities of antioxidant enzymes (SOD, CAT, and GPx) and sexual hormones (FSH, LH, estrogen, progesterone, and testosterone) in both mother rats and their pups if compared with control.  Further, a light microscopic investigation revealed that exposure to HgCl2 during gestation and lactation periods induced deleterious histopathological changes in the ovaries of mothers as well as in the ovaries and testes of their offspring.   Additionally, the ovarian sections from mothers and their offspring displayed weak to negative expression for calretinin antibody, however, the testicular sections from offspring appeared strongly stained with COX-2 antibody (inflammatory marker) and weakly stained with Ki67   antibody (proliferative marker). Further study by flow cytometric technique revealed a highly significant increase in the mean % value of apoptotic cells in both ovaries and testes. On the other hand, co-supplementation of CE to HgCl₂ treated group successfully alleviated the altered antioxidants and hormones as well as the histological changes near to the normal as control.  Conclusion: Celery extract has a powerful ameliorative role against HgCl₂-induced deleterious biochemical and histopathological changes in the gonads of female rats and their pups.