COVID19 has compelled the scientific community to search for an effective drug that can cure; a vaccine or an immunity booster that can prevent the disease. As of now, it is tough to discover a new drug and vaccine discovery is even tougher. Drug repurposing is a shortcut to drug discovery for COVID19. Even this has been proved unsatisfactory. Symptomatic treatment and immunity boosters are only alternatives left. Holy Tulsi (Ocimum sanctum) has been known as an ancient remedy for cure of common cold and respiratory ailment in India vis-a-vis also has been prescribed as one of the recommended ingredients in the immunity booster preparations. The ethanolic extract of aerial parts of Tulsi is reported to contain flavonoids and polyphenolic acids, which are also reported earlier to have anti-viral properties experimentally. Therefore, we undertake the in silico analysis of the phytochemicals as inhibitors of main protease of SARS-CoV-2 virus. The result suggests that the flavonoids and polyphenolic compounds of Tulsi, especially luteolin-7-O-glucuronide and chlorogenic acid may covalently bind to the active residue Cys145 of main protease and irreversibly inhibit the viral enzyme. Further experimental validations are required to establish the theoretical findings.