an injector for vehicles improves utilization rate of air and mixing rate of air and fuel by disposing first and second nozzle holes having different k factors alternately . the injector for vehicles may include a housing of cylindrical shape , a plurality of nozzle holes communicating an inside of the housing with an outside thereof at a lower end of the housing , and a needle adapted to move reciprocally in the housing , and selectively opening or closing the nozzle hole , wherein the plurality of nozzle holes has a plurality of k factors .