1D nanocaterpillar structures were spontaneously formed during the synthesis of fully conjugated poly(2,5-dihexyloxy-1,4-phenylene)-block-polythiophene due to the strong π-π interactions between the polythiophene blocks. With the elongation of the polythiophene block, nanostructures evolved from nanospheres to nanocaterpillars and their length and height increased with good control.