High temperature hydrocarbon sensors are of paramount importance to provide precise control of various combustion processes and directly evaluate the efficiency of catalytic converters. In this study, both p-type La0.67Sr0.33MnO3 (LSMO) and n-type CeO2 nanofibers (NFs) were prepared by electrospinning followed by facile two-step calcination. p-LSMO NFs/n-CeO2 NFs composites with different weight ratios (CeO2 NFs wt%: 0%, 25%, 50%, 70%, 75%, 80%, 90% and 100%) were then prepared by physical mixing with the help of sonication and further were employed as sensing elements to systematically investigate their response to carbon monoxide (CO) and propane (C3H8) at 800 degrees C. Clear p-n transition behaviour was observed from p-LSMO NFs dominated composites to n-CeO2 NFs dominated composites in the presence of targeting gases. At the specific p-LSMO NFs/n-CeO2 NFs composition (CeO2 NFs wt% = 70%), the sensor exhibited an opposite response direction to CO and C3H8 which offers a simple way to differentiate them. Moreover, the p-LSMO NFs/n-CeO2 NFs composite with the CeO2 NFs content of 80% showed good sensitivity and selectivity to C3H8 over other reducing gases such as CO and CH4 at a high operation temperature of 800 degrees C. The mechanisms of enhanced selectivity and p-n transition behaviour are also proposed based on the observed experimental results. This study opens an avenue for tailoring the selectivity of high temperature gas sensors by simply tuning the p-n heterojunction.