The association of Pneumocystis jirovecii pneumonia (PJP) with connective tissue disease (CTD) and mycophenolate mofetil's (MMF) potent activity against PJP have been separately reported. Until now, there have been no papers describing the occurrence of PJP following MMF treatment in CTD patients. The objective of this study was to describe the clinical features, risk factors, outcomes of PJP in patients with CTD and investigates the effects of MMF on the occurrence of PJP in China. In this retrospective cohort study, we performed a chart review, analyzing clinical features, treatment, and outcomes of PJP in patients with CTD in a single hospital. A total of 17 cases met the inclusion criteria of having PJP and a CTD diagnosis: systemic lupus erythematosus; polymyositis; dermatomyositis; rheumatoid arthritis; Wegener's granulomatosis; and microscopic polyangiitis. Sixteen patients were treated with glucocorticoids (GCs) plus immunosuppressive drugs. Only one patient had GCs without immunosuppressive drugs. Ten subjects (62.5 %) received MMF (1-1.5 g/day), and all ten had lymphopenia. The mortality rates of MMF and non-MMF patients were 50 and 14 %, respectively. This study is the first report of PJP following MMF plus GC treatment in patients with CTD. CTD itself may be a risk factor for PJP. When CTD patients receiving MMF therapy have low lymphocyte counts and/or CD4 lymphocyte counts <250/µL, we should be care of occurrence of PJP.