Objective: To perform the pharmacognostical screening and determination of antipyretic and antioxidant activity of Cassia occidentalis L. Methanolic seed extract by different in-vitro models. Methods: The different pharmacognostical parameters were evaluated as per standard procedure. Finally, antipyretic (Brewer’s Yeast Pyrexia model) and antioxidant activity (DPPH and Hydrogen Pyrode Method) was evaluated by adopting different methods. Results: The extracts showed a marked antipyretic effect (Figure 1) by causing a reduction in yeast-induced fever. Methanolic extract (400 mg/kg) showed the effect to the same degree as paracetamol (20 mg/kg, i.p.). The experimentally induced laboratory model was employed in evaluating the antipyretic activities of methanolic extracts of Cassia occidentalis L. The extract caused a better hypothermal activity against yeast-induced pyrexia in rats. Free radical scavenging activity of Cassia occidentalis L. was found because polyphenolic compounds present in plant contribute significantly to the total antioxidant capacity of the seed. Flavonoids play some important pharmacological roles against diseases, such as cardiovascular diseases, cancer, inflammation and allergy. Conclusion: The results of the study indicate that the methanolic seed extract of Cassia occidentalis L. possesses strong antipyretic and antioxidant activity. This study described many pharmacognostical features and antioxidant activity of seeds of Cassia occidentalis L. which will give a new direction for the future scientific research.