A bicycle toe positioning device comprises a treadle having a main body which is formed with an axial hole, an axial rod and a bearing set. The treadle is further formed with a first clamping portion and a second clamping portion. A tightening unit has a first positioning end and a second positioning end. In assembly, the first clamping portion is buckled to a rib and a pair of wings of the first positioning end. The second clamping portion is secured to the second positioning end so that the treadle is secured to the toe positioning unit. The first clamping portion has a buckling block which is fixed to the treadle by using an pivotal rod. A spring is retained in the first clamping portion and an adjust unit serves to adjust the tightness of the buckling block.