Manganese chloride (MnCl₂) is a known environmental toxicant that disrupts reproductive hormones and hematological parameters in female Wistar rats through oxidative stress and hormonal dysregulation. This study evaluates the protective potential of cinnamic acid (CA), a phenolic compound with antioxidant and metal-chelating properties, against Manganese chloride induced toxicity. Thirty female Wistar rats were divided into six groups: Group A; control, Group B; Manganese chloride only (10 mg/kg), Group C; Cinnamic Acid low dose (50 mg/kg), Group D; CA high dose (100 mg/kg), Group E; Manganese chloride + Cinnamic Acid low dose, and Group F; Manganese chloride + Cinnamic high dose. Over 90 days, Manganese chloride significantly reduced progesterone (2.45 ± 0.71 ng/mL), estradiol (0.70 ± 0.22 pg/mL), red blood cell count (RBC, 6.35 ± 0.43 ×10¹²/L), hemoglobin (HGB, 11.70 ± 0.77 g/dL), and hematocrit (HCT, 34.03 ± 3.68%), while increasing granulocyte count (GRAN#, 0.60 ± 0.32 ×10⁹/L) (p < 0.05). High-dose CA co-treatment significantly restored these parameters, with progesterone at 17.66 ± 0.46 ng/mL, estradiol at 2.19 ± 0.13 pg/mL, RBC at 7.59 ± 0.46 ×10¹²/L, HGB at 13.50 ± 0.74 g/dL, and HCT at 43.93 ± 8.24% (p < 0.05). These findings suggest CA’s dose-dependent protective effects against Manganese chloride toxicity, warranting further research into its therapeutic applications.