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<i>P</i>-sulfonatocalix[n]arenes have demonstrated a great potential for encapsulation of therapeutic drugs via host-guest complexation to improve solubility, stability, and bioavailability of encapsulated drugs. In this work, guest-host complexes of a third-generation anticancer drug (oxaliplatin) and <i>p</i>-4-sulfocalix[n]arenes (<i>n</i> = 4 and 6; <i>p</i>-SC4 and <i>p</i>-SC6, respectively) were prepared and investigated, using ¹H NMR, UV, Job’s plot analysis, and DFT calculations, for use as cancer therapeutics. The peak amplitude of the prepared host-guest complexes was linearly proportional to the concentration of oxaliplatin in the range of 1.0 × 10⁻⁵ M⁻¹ to 2.1 × 10⁻⁴ M⁻¹. The reaction stoichiometry between either <i>p</i>-SC4 or <i>p</i>-SC6 and oxaliplatin in the formed complexes was 1:1. The stability constants for the complexes were 5.07 × 10⁴ M⁻¹ and 6.3 × 10⁴ M⁻¹. These correspond to complexation free energy of −6.39 and −6.52 kcal/mol for <i>p</i>-SC4 and <i>p</i>-SC6, respectively. Complexation between oxaliplatin and <i>p</i>-SC4 or <i>p</i>-SC6 was found to involve hydrogen bonds. Both complexes exhibited enhanced biological and high cytotoxic activities against HT-29 colorectal cells and MCF-7 breast adenocarcinoma compared to free oxaliplatin, which warrants further investigation for cancer therapy.