Background: Serankottai nei is a popular Siddha drug, used in the treatment of lung infections including tuberculosis, autoimmune joint diseases (rheumatoid arthritis, degenerative osteoarthritis), cancers and neurological pain. Objective: To standardize serankottai nei and to screen its in-vitro antitubercular activity of in H37Rv strain. Materials and Methods: Serankottai nei, a medicated ghee preparation was procured from the SKM Siddha and Ayurveda Co India Ltd, Erode, Tamil Nadu. Unsaponifiable matter (USM) from the ghee preparation was separated and preliminary phytochemical screening was done. Further, USM was dissolved in 10 ml of chloroform and 3 and 6 µl of the above sample was applied for HPTLC fingerprint, which was developed in toluene: ethyl acetate (9.0:1.0). The developed plates were scanned under UV 254 nm, 366 nm, 540 nm and 620 nm post derivatization. R f , colour of the spots and densitometric scan were recorded. Different doses of USM were screened for in-vitro antitubercular activity against H37Rv strain using Alamar Blue Dye method. Results: Phytochemical screening of 8% w/w USM obtained from serankottai nei showed presence of alkaloid, phenol, steroid and terpenoid. In HPTLC, there were 15, 5 and 7 peaks at 254 nm, 366 nm and 620 nm respectively. The Minimum Inhibitory Concentration (MIC) against H37Rv strain of pyrazinamide, streptomycin, ciprofloxacin were 3.125, 6.25 and 3.125 µg/ml respectively. Whereas, the MIC of serankottai nei was 1.6 µg/ml, which was almost 25 to 50% of standard drugs. Conclusion: Serankottai nei has shown promising antitubercular activity in in-vitro study. Thus, Semecarpus anacardium could be a suitable candidate for a new herbal based antitubercular drug.