Abstract: Objective Study the mechanism and treatment of pituitary hyperplasia in preadolescence of children. Method To report three pituitary hyperplasia in children during preadolescence and review literatures. Results All three children during preadolescence present mass in saddle area in MRI, present microsomia and chilly in clinical manifestation. The enlarged pituitary combined with both elevated thyrotrophin stimulating hormone(TSH) and prolactin(PRL) and low thyroid hormone value. All of three children during preadolescence was cured by thyroxine replacement therapy for about a half year. The pituitary size was normal in MRI examination and the clinical symptom had obviously improved and presented normal value in the endocrine examination. Conclusions The diagnosis of pituitary hyperplasia with primary hypothyroidism should be considered when the children daring preadolescence present with the enlargement of pituitary gland combined with both elevated TSH and PRL and low thyroid hormone value, and the pituitary hyperplasia only can be cured by thyroxine replacement therapy,and needn't make a operation.