Two alternative flexible alkyne-linked thymine nucleosides (propargyl-diethylene glycol- or undecyn-linked 5-hydroxymethyluracil derivatives), as well as their phosphoramidites and triphosphates, were designed and synthesized. The nucleoside 3'-O-phosphoramidites were successfully incorporated into oligonucleotides on a solid support, whereas the nucleoside triphosphates served as good substrates for polymerase synthesis of modified DNA, which underwent fast and efficient copper-catalyzed alkyne azide 1,3-dipolar cycloaddition (CuAAC) reactions.