Prolactin-secreting adenoma, which usually presents with amenorrhea and galactorrhea syndrome, is quite rarely diagnosed in the prepubertal age group. We reported a rare case of a prepubertal prolactin-secreting adenoma and discuss its clinical, radiological and histological features. An 8-year-old girl presented with headache, progressive visual deterioration and precocious puberty. The serum prolactin level was 57.8 ng/ml. Computerized tomography and magnetic resonance imaging revealed an invasive suprasellar tumor. The tumor was partially resected through an interhemispheric approach in a first operation, and residual tumor was resected through the right pterional approach in a second operation. The histological diagnosis was a prolactin-secreting adenoma with high cellular pleomorphism. The Ki-67 labeling index was 5.7%, indicating aggressive biological behavior. Postoperatively, the patient was prescribed bromocriptine as maintenance therapy, and the serum prolactin level became normalized. There is a tendency for diagnosis of a prepubertal prolactin-secreting adenoma to be delayed because there are no endocrinological manifestations. Therefore, the tumor tends to become larger and invasive. Although it is rarely experienced, a prolactin-secreting adenoma should be considered in the differential diagnosis of a large, invasive parasellar lesion in the prepubertal age group.