Co-doping with two elements has recently attracted attention as a novel approach for tailoring the semiconductor -metal transition (SMT) characteristics of vanadium dioxide (VO2). Here, we investigate the influence of titanium/yttrium (Ti/Y) co-doping on the microstructure and SMT characteristics of VO2 thin films. At low Y concentration, Ti/Y co-doped VO2 thin films exhibit a monoclinic structure similar to VO2 but characterized by a smaller grain size, whereas, the VO2(B) phase appears as the Y concentration is increased. Interestingly, even a complete amorphization of the film is obtained for co-doped VO2 thin films. The strong dependence of the microstructure upon the co-doping level is ascribed to the conjugated influence from the simultaneous adjustment of V-V chains and V-O bonds due to the existence of Ti4+ and Y3+ ions in VO2 lattice, respectively. As a result, the SMT feature of VO2 thin films is strongly limited or even fully disappears.