To explore the role of dithiocarbamate ester group in hydroxamic acid flotation of cassiterite, a special surfactant S-[(3-hydroxyamino)-propoxy]-N-octyl dithiocarbamate (DTCHA) was designed. With carbon disulfide, octylamine, methyl acrylate and hydroxylamine as raw materials, DTCHA was facilely synthesized by a “one-pot” approach. In situ AFM (atomic force microscopy) clearly captured DTCHA aggregates self-assembled on cassiterite, which significantly increased its surface hydrophobicity. DFT (density functional theory) calculation predicted that the dithiocarbamate ester group possessed the ability of electron-donating and electrostatic interaction, and might be the second reactive center of DTCHA. XPS (X-ray photoelectron spectroscopy) and FTIR (Fourier transform infrared spectra) allowed to infer a bonding interaction between DTCHA’s dithiocarbamate with Sn during DTCHA reaction with Sn(Ⅳ) ions in aqueous solutions, while that with surface Sn(Ⅳ) atoms of cassiterite wasn’t concluded. The attendance of the dithiocarbamate hardly weakened the flotation selectivity of DTCHA against calcite, while its hydrophobization towards cassiterite became much stronger. Thus, DTCHA possessed the stronger collecting power and better selectivity for flotation separation of cassiterite from calcite than octyl hydroxamic acid. Revealing the role of DTCHA’s dithiocarbamate as a hydrophobic group in cassiterite flotation offered a new strategy for designing oxide minerals collector. That was, besides alkyl groups, some sulfhydryl minerophilic groups for sulfide minerals could be designed as preferable hydrophobic groups for oxide minerals flotation.