A novel series of oligomers consisting of thiophene as a p-type unit and oxadiazole as an n-type unit were separately synthesized. On the basis of the characterization of photophysical and electrochemical properties, the structure-property relationships of the oligomers were investigated. Cyclic voltammogram studies showed that changing the number of thiophene and oxadiazole units could effectively modulate the electronic properties of the p-n diblock and triblock oligomers. The effect of molecular regiochemistry on electronic properties is also investigated. The observed electronic properties were consistent with theoretical calculations. These systems serve as excellent examples, demonstrating the band gap control principle in the p-n heterostructure oligomers.