Background: Cassia sophera Linn is a medicinally important plant belonging to the family of Caesalpiniaceae. The whole part of the plant is used as traditional folk medicine and is reported to possess analgesic, anticonvulsant, antioxidant, anti-inflammatory, hepatoprotective, and antiasthmatic activity. The present communication attempt is to evaluate fatty acids from different parts of the plant by GC-MS spectrophotometer and total protein content by the Kjeldahl method and to quantify some active constituents, i.e., alkaloid, saponin, and flavonoid. Results: From fatty acid compositions of the petroleum ether extract of leaves, stems, flowers, and seeds of this plant grown in Bangladesh, 22 compounds from leaves, 8 compounds from stems, 9 compounds from flowers, and 12 compounds from seeds were identified. The main fatty acid was arachidic acid (38.66%) from leaves. Linoleic acid (40.12% and 42.40%) was found mainly from stems and seeds, whereas from flowers, it was docosadienoic acid (27.14%). Conclusion: The findings from the present study showed that the protein content for seeds has higher value (19.20%) than other parts of the plant. Also the present investigation showed that different parts of the plant contain phytochemicals in appreciable quantities in the form of flavonoids, alkaloids, and saponins. The flavonoid and alkaloid content of leaves showed higher value. But the stem part showed higher saponin content than other parts of the plant.