1. objectives. To compare the efficacy and the safety of mometasone furoate nasal spray (MFNS; Nasonex 200μg, daily) alone versus a combination with montelukast (singulair 10mg, daily) in chronic rhinosinusitis (CRS) with asthma after functional endoscopic sinus surgery (FESS) for improvement the clinical control of CRS
2. the clinical hypotheses. The investigators hypothesize that postoperative combined montelukast and MFNS can better improve clinical control of CRS concomitant with asthma after FESS compared with MFNS alone.
3. study design This study is a 9-month randomized, open-label, controlled interventional study.

1. Surgery plan

   • Pre-operation: Patients enrolled in the study will complete assessment and specimen collection on the first day, then followed by 1 week drug therapy with prednisone (30 mg once daily) and MFNS(200ug, once daily).
   • FESS: For patients with no surgical contraindications, FESS will be performed. Bilateral nasal cavities will be filled with swelling sponges postoperatively. The stuffing will be removed on postoperative day 2. The patients will be discharged on day 3 after surgery.
   • Other treatment: All patients will receive nasal irrigation (normal saline 500 mg twice daily) from postoperative day 3 until day 30. Asthma will be treated as the guidance of professors from the Department of Respiratory Medicine in the investigators hospital.

2. Drug treatment phase Three days after the surgery (FESS) described above, all patients will be assigned to the following two groups (30 patients each group) using random numbers generated by statistical software.

   • Experimental group: Montelukast (10mg, once daily) and MFNS (200μg, once daily) for 6 months
   • Control group: MFNS (200μg, once daily) for 6 months

3. Follow up After the 6-month drug treatment phase, there are still a 3-month follow-up. Totally, there are 5 visits after FESS surgery.

   • Visit 1: baseline
   • Visit 2： Day 31 post-FESS
   • Visit 3: Day 61 post-FESS
   • Visit 4: Day 91 post-FESS
   • Visit 5: Day 181 post-FESS
   • Visit 6: Day 271 post-FESS

Inclusion Criteria:

1. Diagnosis of chronic rhinosinusitis according to European position paper of rhinosinusitis and nasal polyps 2007
2. Diagnosis of asthma based on Global initiative for asthma 2012
3. All patients should provide informed consent prior to the study and agree to follow-up appointments.

Exclusion Criteria:

1. Immunodeficiency diseases, history of head and/or facial trauma, cancer or organ transplant recipients.
2. Pregnancy or lactation.
3. Uncontrolled bronchial asthma.
4. Acute respiratory tract infection within one month before the study.
5. Use of leukotriene receptor antagonist within 3 months before the enrollment.