Abstract: Background: Myasthenia gravis is a rare disease that affects the respiratory muscles with mechanical ventilator support. Multimodalities of respiratory therapies may reduce or prevent such those complications, thereby improving gas exchange and airway clearance. Purpose: To explore the effect of multimodality chest physiotherapy on myasthenia gravis patients' clinical outcomes. Design: A quasi-experimental research design was utilized. Sampling: A purposive sample of 80 adult patients were selected. Patients are equally divided into A: control and B: intervention groups. Setting: The study was conducted at Neurological Intensive Care Units at Tanta University Hospital. Instruments: One instrument was used to collect data and it consisted of 4 parts. Results: No significant relation between both groups in relation to demographic data and clinical data. Mean of respiratory rate in the group A increased from 1st d to 7th d with a significance difference (p <0.001). In the group B, the mean of respiratory rate was decreased to 21.0±2.13 in the 7th d at significance difference (p <0.001). Regarding oxygen saturation, the mean of Spo2 in group A in 7th d was 89.95±16.80, while in the group B was 95.95±16.80 at significance difference (<0.001). Conclusion: In myasthenia gravis patients, multimodality chest physical therapy aided to improve respiratory status and oxygenation parameters. Recommendations: Health education should be provided to nurses about use of a manual chest vibrating device and other chest physiotherapy procedures.