Submucous cleft palate (SMCP) is a type of cleft lip and/or palate that is often diagnosed based on speech symptoms caused by velopharyngeal insufficiency and is frequently accompanied by complications. Although both surgery and speech therapy are treatment options, reports vary according to appropriate timing and suitability. At our hospital, patients who opted against surgery underwent speech therapy with positive results. This study aimed to evaluate the progression of velopharyngeal function (VPF) over time in non-operated patients with SMCP to formulate a new treatment approach. Fifty-three patients with SMCP who underwent VPF evaluation and over 1 year of speech therapy at the Cleft Lip and Palate Center of Aichi Gakuin University Dental Hospital between 2002 and 2022 were included. The patients were classified into with-complications and without-complications groups, and data on VPF evaluation, therapy duration, and progress were collected. Twenty patients experienced complications, while 33 did not. In the without-complications group, a significant improvement in VPF was observed after speech therapy. At the lowest VPF, five patients required surgery, but by the final evaluation, all patients experienced improvements, with no case of "poor." Conservative treatment through long-term speech therapy demonstrated significant improvement in velopharyngeal function for non-complicated SMCP cases, suggesting it as a viable alternative to surgery in selected patients. This study highlights the clinical relevance of conservative speech therapy as a cost-effective, accessible alternative to surgery, particularly in resource-limited settings, offering comparable outcomes in non-complicated SMCP cases and potentially reducing healthcare burdens.