New s-triazine derivatives 13a–h were synthesized for the structure–activity relationship studies as potent anticancer agents. The prepared analogues were evaluated for their in vitro inhibitory activity against the growth of PA-1 (Ovarian cancer), A549 (Lung cancer), MCF-7 (Breast cancer), and HT-29 (Colon cancer). Tri-substituted s-triazine derivatives (13e–h) with morpholino group on s-triazine scaffold exhibited potent anticancer activities compared to di-substituted s-triazine derivatives. Compounds 13e–h also showed relatively selective PA-1 and HT-29 cancer cell inhibition over other cancer cell lines. Structure–activity relationships provided useful insights in these classes of compounds and paved the way to design novel analogues with more potency.