Background: Turbinaria conoides, a brown seaweed, is a rich source of oxygenated fucosterols which are capable of suppressing the proliferation of cancer cells. Their specific therapeutically significant biological activity is directly related to the unique structural features of the molecule. This study specifically focuses on extracting unconventional sterol molecules (side chain extension) from this seaweed which can be used as a lead molecule to evolve therapeutical agents. Materials and Methods: To isolate unconventional sterol molecule, for structural elucidation and bioactivity study, sufficient amount of T. conoides was collected from Mandapam, an unique biodiverse environment along the Southeast coast of India. State-of-the-art methods available for the purification and characterization of molecule (High-resolution fast-atom bombardment mass spectrometry, ultraviolet-visible spectroscopy, attenuated total reflection–fourier transform infra-red, One-dimensional nuclear magnetic resonance, and two-dimensional nuclear magnetic resonance) were put in. In vitro bioassays (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium bromide, double staining, and flowcytometry) were carried out against A549 and human liver cancer cell line (HepG2) malignant cells to assess the cytostatic potential. Data were statistically validated. Results: A unique unconventional sterol molecule (Turbiconol) with ethyl and methyl group at C-27 was isolated. This molecule induced apoptosis in A549 and HepG2. However, cell cycle assessment revealed G0/G1 cell cycle arrest in Hep G2 and G2/M checkpoint was responsible for the suppression of A549 cell line. Conclusion: A novel unconventional compound, turbiconol, is reported in this study. In vitro results highlight the potential of this molecule in developing therapeutical combination which can be used for novel treatment methods.