Hemp fiber is an excellent sustainable and renewable alternative to glass fiber as a reinforcing component in composite system, owing to its unique features of fast growth, high mechanical strength, low density, low cost, biodegradable, and low energy consumption. In this study a systematic investigation of physical and chemical treatment on hemp fiber was conducted, and their effects on thermal stability of hemp fiber were analyzed. Oxygen plasma treatment was used as physical modification approach, 5 wt% sodium hydroxide solution was used for chemical modification. Surface chemical composition and thermal stability were characterized by Fourier transform infrared spectroscopy and thermo gravimetric analysis. The results indicated that 5 wt% of NaOH with 16 hours treatment time increased hemp fiber thermal stability, while the plasma treatment had no impact on thermal stability of hemp fiber.