Rheumatoid arthritis (RA) is an autoimmune disease of multifactorial etiology, characterized by a chronic inflammatory reaction of the joints, but can also affect other tissues. Some environmental factors can trigger an immune system response in genetically susceptible individuals, activating the disease. Lower diversity of gut microbiota, and dysbiosis, have been observed in RA patients. In this regard, approaches to decrease inflammation, and to restore the microbiota, have been suggested. These include oral administration of single probiotics, or probiotic mixtures, on their own, or in combination with drugs. Vitamin K (VitK) is one of the many products of the intestinal microbiota. Lower levels of some forms of VitK have been measured in the serum and stools of RA patients and some studies have found an inverse correlation between VitK levels and the clinical severity of the disease. Additionally, some forms of this vitamin, when given orally, have been shown to exert positive effects in decreasing RA activity, and delaying its onset and progress. This review aims at describing the link between the gut microbiota and RA, focusing on the role of VitK and probiotics as possible adjuvant therapies in this disease.