Abstract: This invention relates to a collapsible bicycle and in particular to one including a top tube, a seat tube pivotally connected with one end of the top tube, a down tube pivotally connected at the lower end with a lower end of the seat tube and being collapsible at the intermediate portion, a reinforcing tube pivotally connected at the upper end with an intermediate portion of the top tube and having at the lower end two rollers and a spring-loaded positioning member adapting to groove and the recess of the down tube respectively, a head tube fixedly connected with down tube and pivotally connected with the top tube, a handlebar composed of a major bar and an auxiliary bar, and two crank arms pivotally connected with an axle of the bicycle and being able to be folded in alignment with center of the axle.