A stereo-selective palladium-catalyzed one-pot Tsuji-Trost reaction was used to prepare four β-thiogalactosides from unsaturated D-galactal and thiol. Their structures were characterized by nuclear magnetic resonance spectra and high-resolution electrospray ionization mass spectra. The absolute configuration was confirmed with a Flack parameter of 0.019(15) by X-ray crystallography using a Cu radiation source. Compound 6a (C₂₁H₂₄O₄S): orthorhombic system, space group P2₁2₁2₁, a = 9.0919(4), b = 9.6313(4), c = 22.5936(11) Å, V = 1978.45(15) ų, Z = 4, F(000) = 792, D_c = 1.250 g/cm³, μ = 1.636 mm⁻¹, R = 0.0478 and wR = 0.1384 for 3621 independent reflections (R_int = 0.0390) and 3326 observed ones (I > 2σ(I)). 3-(4,5)-Dimethylthiazol-2-yl-2,5- diphenyltetrazolium bromide (MTT) cell viability assays indicated that these thiogalactosides showed anti-proliferative activities against human gastric cancer HGC-27 cells with IC₅₀ values of 69~88 μM.