Background: The most effective treatment of immune checkpoint inhibitors (ICIs) is restricted in microsatellite instability (MSI-H) subsets of advanced colorectal cancer, but MSI-H only accounts for 4-5% among them. Currently, Fruquintinib/ Regorafenib is the standard third-line treatment for metastatic colorectal cancer (mCRC) with microsatellite stable (MSS), which efficacy remains limited in pre-clinical trials. According to the published literature, ICIs has little efficacy in the treatment of refractory advanced mCRC patients with MSS. However, there may be a good synergistic mechanism in the combination of ICIs and anti-VEGFR drugs, which can improve the tumor microenvironment (TME). Our study aimed to evaluate the efficacy and safety of Fruquintinib plus Toripalimab as third-line treatment for refractory advanced mCRC. Methods: This was a single-arm, single-center, phase II clinical trial with 30 patients. Pts received toripalimab (240mg, i.v., Q3W), combined with Fruquintinib (5mg, p.o., 3 weeks on/ 1 week off) until the disease progresses/unacceptable toxicity or receiving the above two drugs as maintenance treatment. The primary endpoint was objective response rate (ORR); the secondary endpoints were disease control rate (DCR), 1-year progression-free survival (PFS) rate, overall survival (OS) and safety. Results: As of Feb 5, 2022, 24 mCRC pts (female: 29.2%, median age: 52.1 years) with ECOG PS ≤ 2 who failed to at least 2 previous lines of therapy containing fluoropyrimidine, oxaliplatin or irinotecan combined with Bevacizumab or Cetuximab were enrolled. The ORR was 16.7% (95% CI：59.7%-94.8%). The DCR was 54.1%, including 4 patients with PR and 9 patients with SD, respectively. 16 patients were alive and the study treatments for 6 patients were still ongoing. Median PFS was 6.0 months (95% CI：3.511-12.489), the 1-year PFS rate was 18%; median OS was 8.0 months (95% CI：1.452-10.548). Overall, 24 pts were enrolled for safety analysis, The most frequent treatment related adverse events were fatigue (50%), hepatocyte dysfunction (36.3%), hypertension (29.1%) and abdominal pain (27.0%). 6 patients (25%) experienced grade 3/4 TRAE (including hypertension, liver enzyme elevation, and immune-associated pneumonia). No treatment-related death was reported. TRAEs leading to either Fruquintinib or Toripalimab discontinuation occurred in 3 (12.5%) pts each. Conclusions: Fruquintinib plus Toripalimab showed certain efficacy and favorable safety profile in refractory advanced mCRC with MSS. It may provide a new choice for mCRC patients who are receiving third-line treatment. The results supported ongoing combined treatment in mCRC patients with MSS and more data will being updated subsequently. Clinical trial information: ChiCTR2000028965.