This is a single arm Phase II study with a safety run-in to identify the recommended phase II dose of the combination therapy of atezolizumab and guadecitabine. Patients with recurrent/advanced urothelial carcinoma (stage IV) who had previously progressed on check-point inhibitor therapy with PD-1 or PD-L1 targeting agents are eligible for this study. After a dose that is safe and tolerable has been established, a dose expansion phase (Phase II) will begin. This study will enroll a total of 4 to 53 patients depending upon the number of patients treated in the safety run-in phase and the number of subjects replaced during the phase II portion.