The Napier grass continues to be a popular forage crop in Nakhonsawan Province and other areas in the northern and east-northern parts of Thailand. Increasing the growth and biomass of Napier grass growing in low-quality sandy soil will increase the economic value of this plant. The stem cutting of two cultivars of Napier grass, cv. Pakchong 1 (Pennisetum purpureum x Pennisetum americanum) and sweet grass (Pennisetum purpureum cv. Mahasarakham), were exposed to two plant growth regulators, gibberellic acid and salicylic acid, and two application methods, soaking for 24 hr and watering after inoculation into the soil, were studied. For one plant growth regulator test, the most appropriate concentration of gibberellic acid and salicylic acid were 0.01 and 100 mg/L, respectively, for the soaking and watering method. There was an interaction between the combination of plant growth regulator type and application method for both cultivars. The best stimulation effect for sweet grass was soaking with 100 mg/L salicylic acids only. The response of Napier grass cv. Pakchong 1 was different. Soaking with 0.01 mg/L gibberellic acid and watering with 0.01 mg/L gibberellic acid was suitable for increasing shoot and root length while soaking with 0.01 mg/L gibberellic acid and watering with 100 mg/L salicylic acid was suitable for increasing fresh and dry weight. This information will be useful for stimulating the growth of Napier grass in agricultural purposes.