Abstract. Head and neck malignant tumors have numerous locations of the disease. After patients receive radiotherapy, their nutritional status is very poor, thus the curative effect is unsatisfactory. The aims of the present study were to investigate and analyze the nutritional status of patients with head and neck cancer undergoing radiotherapy (RT) in order to provide positive nutrition intervention for assisting the radiotherapy effect. A total of 40 patients with head and neck cancer were selected using a method of subjective global assessment (SGA) to assess nutritional status, including calorie intake and energy expenditure. In a randomized, controlled study, 20 patients received intensive dietary counseling and nutritional therapy (G1) and 20 received regular dietary as controls (G0) preradiotherapy and postradiotherapy. The primary endpoint was calorie intake and energy expenditure. The secondary endpoint was SGA rating with nutritional therapy. At the end of RT, energy intake showed a net increase in G1 (1,691±301 kcal) compared with that in G0 (1,066±312 kcal) (P<0.05); energy expenditure increased in G1 (1,673±279 kcal) compared with G0 (1,490±298 kcal) (P<0.05). The prevalence of severe malnutrition following radiotherapy was significantly different between the two study groups (10 patients in G0 and 4 patients in G1; P<0.05). The number of the normal malnutrition patients postRT in G0 decreased from 4 to 2 and conversely, in G1 it increased from 3 to 6 (P<0.05). In conclusion, patients with head and neck cancer were most malnutritioned, which impacted on clinical outcome. Timely nutritional intervention can effectively prevent weight loss and muscle wasting.Additionally, it may improve quality of life by decreasing the frequency of severe malnutrition.