Pseudoachalasia is a disorder in which symptoms, radiologic, endoscopic, and manometric results resemble idiopathic achalasia. Although these diagnoses may appear similar, their underlying causes and therapy differ significantly. Pseudoachalasia is frequently associated with malignancy, particularly primary adenocarcinoma of the esophagus or cardia. We present a 75-year-old female patient with metastatic osteosarcoma who presented with symptoms of dysphagia and typical esophageal manometry findings of achalasia. Esophagoscopy showed resistance while crossing the gastroesophageal junction. Abdominal computed tomography showed a mediastinal mass. An endoscopic ultrasound was performed, and a fine needle biopsy was taken from mediastinal deposits. Histopathology, which showed signet cell tumor cells. As the cancer was inoperable, chemotherapy was started and her symptoms have decreased from before. Typical esophageal dysmotility can be seen in pseudoachalasia, a secondary type of achalasia caused mostly by cancer or benign tumors, surgical complications, or paraneoplastic disorders. Hence we can conclude diagnosing pseudoachalasia earlier can improve outcomes.