A comprehensive discussion on phytosterol composition, metabolism, functions, precursor roles and mechanism of action are given in this book. Another key aspect of the study constitutes difference of faces of antioxidant capacity of an array of free and conjugated phytosteroids of Solanum xanthocarpum and Solanum nigrum, and withasteroids of Withania somnifera has been assessed. Four standard sets of assays, namely, reduction of ABTS, DPPH, FRAP and superoxide radical, have been used. The contribution, in this regard, of metal ions, naturally-complexed with the phytosteroids and withasteroids, has also been evaluated. The findings suggest the contribution of naturally occurring metallo-organic complexes in human well being. The mechanisms suggested for the antioxidant actions of the compounds project the role of molecular architecture of free and conjugated steroids. This study is not at all yet another experiment of antioxidant activity of phytosteroids. Here, it involves the key feature that metal ion conjugation improves the bioactivity of phytosteroids which was manifested in the antioxidant assay systems. This aspect was never been dealt before.