Background: Ramucirumab (RAM) plus FOLFIRI has been considered as the standard care of second-line treatment in metastatic colorectal cancer (mCRC). However, there have been few data which prospectively evaluated the efficacy and safety of RAM or other anti-VEGF drugs plus FOLFIRI after anti-EGFR antibody therapy in RAS wild-type mCRC. We therefore investigated the efficacy and safety of RAM plus FOLFIRI as second-line treatment in patients with RAS wild-type mCRC previously treated with oxaliplatin-containing chemotherapy with anti-EGFR antibody. Methods: The JACCRO CC-16 was a multicenter, phase 2 trial to evaluate the efficacy and safety of RAM (8 mg/kg) plus FOLFIRI (irinotecan 150 mg/m², bolus 5-FU 400 mg/m², infusional 5-FU 2400 mg/m²) in mCRC patients with RAS wild-type tumors and ECOG PS 0 or 1, after first-line doublet or triplet plus anti-EGFR antibody therapy. The primary endpoint was 6-month progression-free survival (PFS) rate. The secondary endpoints included PFS, overall survival, objective response rate (ORR), early tumor shrinkage (ETS), and safety. We hypothesized a threshold 6-month PFS rate of 30% and an expected 6-month PFS rate of 45% for the protocol treatment. A sample size of 74 patients was required (one-sided α, 0.05; β, 0.2). Results: A total of 92 patients were enrolled between October 2018 and December 2020. Ninety-one patients, excluding one ineligible patient, were analyzed as the full analysis set: median age 66.0-y (range, 29–84), 46% female, 81% ECOG PS 0, 40% with primary tumor, 95% left-sided (rectum, sigmoid or descending colon) primary tumors, 70%/42% with liver/lung metastases. In prior first-line treatment, 19 (21%) patients were treated with triplet plus anti-EGFR antibody. The median number of treatment cycles was 10 (range, 1–56). Primary endpoint was met; at data cut-off, with 76 events, 6-month PFS rate was 58.2% (95% CI; 47.4-67.6). The median PFS was 7.0 months. The ORR, disease control rate, and ETS were 10.7%, 86.9%, and 16.9%, respectively. In the safety population of 92 patients, any grade adverse events (AEs) were neutropenia (75%), hypertension (59%), proteinuria (34%), and diarrhea (33%). Grade 3-4 AEs were neutropenia (48%), hypertension (27%), proteinuria (4%), diarrhea (3%), and febrile neutropenia (3%). No treatment-related death was observed. Conclusions: This is the first prospective study to demonstrate that RAM plus FOLFIRI as second-line treatment has favorable PFS rate and tolerability after anti-EGFR antibody containing chemotherapy in RAS wild-type mCRC patients. Clinical trial information: jRCTs061180002.