In the present study, the effects of bulb type palatal lift prosthesis (bulb-PLP) therapy on nasality and velopharyngeal function (VPF) of patients with velopharyngeal incompetence (VPI) following palatoplasty were longitudinally assessed.The subjects included 18 patients (3 to 52 years of age) who had shown persistent VPI following palatoplasty and who had received bulb-PLP therapy. Nasality and VPF were assessed by perceptual voice analysis, nasometer test, blowing test, and cephalometric radiographic examination. Based on the outcomes of bulb-PLP therapy, the subjects were classified into two groups: the effective group and the ineffective group. Furthermore, the obturating and VPF-activating effects by bulb-PLP therapy were analyzed, and factors relating to different VPF activities were determined.All subjects achieved adequate VPF by wearing a bulb-PLP. After treatment, 10 patients (55.6%) achieved successful activation of VPF without bulb-PLP (the effective group), while persistent VPI remained in 8 patients (the ineffective group). The beginning-blowing ratio of the effective group was significantly greater than that of the ineffective group (P < 0.05) and the velopharyngeal distance (V-P distance) of the effective group tended to be smaller (P = 0.07). Regarding the shape of the bulb head, the angular type was dominant in the ineffective group, while the round type was dominant in the effective group.Bulb-PLP therapy was useful for providing adequate VPF activation. Possible signs of the subsequent effective activation of VPF are considered to be: 1) preexisting adequate VPF on blowing, 2) smaller V-P distance, and 3) synchronized palatopharyngeal movement.