Abstract We report on the fabrication and characterization of low-dimensional single crystals of hexyl-substituted thiophene/phenylene co-oligomer, 5,5′-Bis(4′-n-hexyl-4-biphenylyl)-2,2′-bithiophene (BP2T-Hx). X-ray diffraction measurements of the single crystals reveal that BP2T-Hx molecules crystallize in a monoclinic form. Temperature dependence of photoluminescence (PL) decay profiles of the BP2T-Hx crystal results in a PL quantum yield of 39%. Above an excitation threshold of 262 μ J cm −2 , amplified spontaneous emission is obtained in a disk-shaped crystal of BP2T-Hx based on the self-waveguiding effect of fluorescence light. Owing to two-dimensional light confinement supported by high group refractive index of 3.4 and high quality factor of 3800, the one-dimensional needle crystal with a cavity length of 70 μ m realizes a Fabry–Pérot lasing at a threshold of 186 μ J cm −2 which is 29% lower than that of the disk-shaped crystal.