While tumor necrosis factor (TNF) inhibitors have dramatically improved the clinical outcomes of rheumatoid arthritis (RA) in recent years, infectious complications are a serious concern. Adalimumab (ADA) is a newly-developed human monoclonal antibody against TNF-alpha. Here we report 2 cases of pneumocystis pneumonia (PCP) which developed in RA patients during ADA therapy. One patient is a 66-year-old woman who had a history of RA for 6 months. The patient was given ADA at 40 mg biweekly for her active arthritis which had been refractory to 6 mg/week of methotrexate (MTX), and 5 mg/day of prednisolone (PSL). One hundred and six days later, she was admitted to our hospital because of fever, cough, and dyspnea. Another patient is a 62-year-old man who had a history of RA for 3 years. Since his arthritis was so active even under the treatment with MTX (8 mg/week) and PSL (15 mg/day), the patient started to be given ADA at 40 mg biweekly. After 28 days, the patient was admitted to the hospital because of dyspnea. Chest roentgenogram and computed tomography revealed interstitial pneumonia in both patients. Beta-D-glucan levels were so high in their serum suggesting the diagnosis of PCP, which was confirmed by the detection of Pneumocystis jirovecii DNA in the sputa by polymerase chain reaction. The patients were immediately treated with sulfamethoxazole/trimethoprim and high-dose prednisolone, which successfully improved pneumonia, and they were discharged from the hospital on the 8(th) and 16(th) day, respectively. PCR and β-D-glucan were useful for the early diagnosis of PCP and lead to the timely induction of adequate treatment and the rescue of these patients.