Recently, the synthesis of P3HT with high head-to-tail regioregularity and the control of the molecular weight have been achieved. Herein, we evaluated the structure in thin films of various molecular weight P3HT (from M-w = 13 k to 828 k) prepared under diverse conditions through X-ray diffraction measurements. Higher molecular weight P3HT had the increase of "Face-on" structure in the thin films. From the structure of thin films prepared under other conditions, the main attribution was the speeds of sedimentation and inhabitation of the crystallization. Moreover, at the surface, the P3HT thin films with high molecular weight (M-w = 828 k) emerged "Edge-on"-rich structure. With the larger distance from thin film surface, the structure gradually changed from "Edge-on" to "Face-on". These fundamental results would lead the suggestion in fabrication and performance of organic electronic devices. (C) 2017 Published by Elsevier Ltd.