To compare the differences of fecal microflora between constipated and non-constipated healthy children, and evaluate the efficacy of probiotics in reducing symptoms of constipation and the influence of intestinal microflora in children with functional constipation.

The investigators performed a monocentric, prospective, randomized controlled trial including 120 pediatric patients (aged 6 months - 10 years old) with functional constipation and 30 healthy age-matched healthy children as control. The investigators shall evaluate the children according to the Rome III Diagnostic Criteria for functional constipation.

The 120 enrolled patients are randomized in to two groups: Group A receiving magnesium oxide and probiotics (MIYAIRI-BM), Group B receiving only magnesium oxide. Each patient is assigned the evaluation constipation symptoms and detection of microflora (beneficial and harmful bacteria) in fecal samples at the enrollment, 4 weeks, and 12 weeks. Patients who take less than 80% of the appropriate dose of medications are withdrawn from the study. All patients included in the study will be given informed oral consent before entering the study.

The data of the fecal microflora evaluated in 60 healthy children are used as control.

Inclusion Criteria:

Rome III Diagnostic Criteria for functional constipation for children aged 6 months - 4 years old is as the following:

1. Two or fewer defecations per week.
2. At least one episode per week of incontinence after acquiring toileting skills.
3. History of excessive stool retention.
4. History of painful or hard bowel movements.
5. Presence of a large fecal mass in the rectum.
6. History of large-diameter stools that may obstruct the toilet. Children aged 6 months - 4 years old is evaluated as functional constipation if two of the situations mentioned above lasted for one month.

Rome III Diagnostic Criteria for functional constipation for children aged 4 years old and above is as the following:

1. Two or fewer defecations in the toilet per week.
2. At least one episode of fecal incontinence per week.
3. History of retentive posturing or excessive volitional stool retention.
4. History of painful or hard bowel movements.
5. Presence of a large fecal mass in the rectum.
6. History of large diameter stools that may obstruct the toilet. Children aged 4 years old and above is evaluated as functional constipation if two of the situations mentioned above happens at least once per week

Exclusion Criteria:

1. gastroesophageal reflux disease
2. inflammatory bowel disease
3. cardiopulmonary diseases
4. liver disease
5. renal disease
6. genetic diseases
7. endocrinal diseases
8. received abdominal surgeries

3 months