The aim of this study was to clarify the association of clinical characteristics of unexplained syncope with the outcome of the head-up tilt test (HUT) in children. A total of 47 patients with unexplained syncope were classified into two groups according to their outcomes of HUT: the positive response group and the negative response group. We reviewed their clinical data as well as the results of HUT and analyzed them with logistic regression method. The results showed that the incidence of positive responses to HUT was higher in girls than in boys (8/22 vs 10/7, p < 0.05). Compared with fainted children younger than 12 years of age, 12- to 16-year-old adolescents with unexplained syncope had a high positive outcome of HUT (30 vs 72.9%, p < 0.05). Compared with fainted children with negative response of HUT, children with positive response to HUT often had syncope in special circumstances (e.g., prolonged standing, anxiety and fright, and morning exercise), and they often had prodrome, such as pallor, lightheadedness, and nausea (28/30 vs 8/17, p < 0.05). However, the number and duration of syncopal spells did not relate to the positive responses to HUT. The logistic regression analysis showed that three factors significantly influenced the outcome of HUT: predisposing factors of syncope, prodrome of syncope, and age (p < 0.05; OR = 32.9434, 17.7281, and 2.7842, respectively). Hence, if pubertal girls with unexplained syncope had clear predisposing factors and prodromes, they were likely to have positive responses to HUT, and they were likely to be clinically considered as having vasovagal syncope.