Abstract: TC4 titanium alloy welded joints were remelted by oscillated laser welding, and effect of oscillated frequency on porosity, microstructure, and mechanical properties of TC4 titanium alloy welded joints was studied. The results showed that remelting oscillated laser welding could effectively eliminate porosity defects of TC4 titanium alloy welded joints. With the increase of oscillated frequency, effect of eliminating porosity was enhanced, and elimination effect of large porosity became more pronounced. In remelting oscillated laser welded joint, microstructure of weld was acicular α' martensite and part of α phase, and microstructure of heat-affected zone was composed of primary α phase, acicular α' martensite and β phase. With the increase of oscillated frequency, stirring effect of laser on molten pool was enhanced, grains in weld gradually broke and became finer, while grains growth in heat-affected zone became more favorable and grains gradually became coarser. The increase of oscillated frequency changed microstructure of welded joints and lead to performance variation of welded joints. Increasing oscillated frequency changed microstructure of welded joints changed, and then changed mechanical properties of welded joints. With the increase of oscillated frequency, hardness in weld of TC4 remelting welded joints increased, while hardness of heat-affected zone gradually decreased, and tensile properties of welded joints showed a downward trend. When oscillated frequency increased to 120 Hz and 150 Hz, fracture area changed from base metal to heat-affected zone.