This article focuses on the growth and transport properties of organic single-crystalline p-n junction nanoribbons. The development of organic nanoelectronics requires the fabrication of organic nanometer-sized p-n junctions for high-performance devices and integrated circuits. Here we demonstrate the formation of single-crystalline p-n junction nanoribbons of organic semiconductors by selective crystallization of copper hexadecafluorophthalocyanine (F16CuPc, n-type) on copper phthalocyanine (CuPc, p-type) single-crystalline nanoribbons. The crystallization of F16CuPc onto CuPc requires several parameters, including similar molecular structures, similar lattice constants, and pi-stacking along the nanoribbon axis. Ambipolar transport of the p-n junction nanoribbons was observed in field-effect transistors with balanced carrier mobilities of 0.05 and 0.07 cm(2) V-1 s(-1) for F16CuPc and CuPc, respectively. A basic p-n junction nanoribbon photovoltaic device showed current rectification under AM 1.5 simulated light. The discrete p-n junction nanoribbons may serve as ideal systems for understanding basic charge-transport and photovoltaic behaviors at organic-organic interfaces.