This article presents the optimization and systematic analysis of the growth kinetics of fiber formation of the regio-regular poly (3-hexylthiophene), rr-P3HT. In addition to it a comparative study of as-prepared fiber with fresh, quenched (at −7°C) and commercial rr-P3HT formed in toluene solvent. The rr-P3HT (Mw ≈ 5340; polydispersity ≈ 1.22) is synthesized using a well known Grignard metathesis reaction and characterized by 1HNMR and FTIR techniques. The films obtained by the ageing of rr-P3HT solution for 20 days contain nanostructured fiber with 6–10 nm thickness. However, it acquires a nanostructured globular shape when same concentration of solution is sudden quenched at −7°C. A saturation point for the growth of nano fiber is observed under UV–visible study and it is found that 10 days are sufficient for fiber growth. The concentration dependent free exciton band width of fiber growth is studied by Frank–Condon principle and correlated with AFM morphological studies. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40931.