A retrospective analysis of the clinical manifestations, laboratory indicators, endoscopic pathology, and lymphoscintigraphy characteristics of a 5-year-7-month-old child with Primary Intestinal Lymphangiectasia (PIL) was conducted, along with a follow-up of treatment outcomes. The child presented with symptoms of diarrhea, abdominal bloating, and tetany in hands and feet. Laboratory tests revealed severe hypoalbuminemia (16.4 g·L^-1), low IgG (2.32 g·L^-1), lymphocytopenia (0.82×10⁹/L), and hypocalcemia with hypomagnesemia. Imaging studies indicated multiple serous effusions, and gastrointestinal endoscopy showed diffuse white, snowflake-like substances on the mucosa of the duodenum and terminal ileum. Pathology demonstrated lymphatic dilation with inflammatory cell infiltration. Characteristic findings from ⁹⁹Tc^m-DX lymphoscintigraphy indicated persistent imaging of the left venous angle, suggesting obstruction at the thoracic duct outlet. Treatment with a low-fat, high-protein, high-medium-chain triglyceride (MCT) diet combined with albumin infusion led to a significant increase in albumin levels to 26.8 g·L^-1 after 7 days, with a marked alleviation of symptoms. The main clinical manifestations of primary intestinal lymphangiectasia in children include diarrhea, abdominal bloating, edema, hypoproteinemia, and electrolyte disturbances. Lymphoscintigraphy confirmed the key pathological mechanism of thoracic duct obstruction, providing a reliable imaging basis for the etiological diagnosis of the disease.