Background: Infliximab is a human-murine chimeric monoclonal IgG antibody against tumor necrosis factor that is used in combination with methotrexate for the treatment of moderate to severe rheumatoid arthritis (RA). The trough concentration of serum infliximab required to control disease activity in RA is \ge1 \mug/mL, and we investigated whether this trough concentration can predict the effectiveness of RA treatment. Methods: We retrospectively analyzed the cases of 76 patients with RA. The REMICHECK Q® (REMIQ) is a kit that can check for serum infliximab concentrations. Infliximab concentrations >1 \mug/mL at 14 weeks after an initial infliximab induction is considered REMIQ-positive, otherwise considered REMIQ-negative. Here, we determined the retention rates and investigated the clinical and serologic features of REMIQ-positive and REMIQ-negative patients. Results: At 14 weeks, significantly more of the REMIQ-positive patients (n = 46) were responders compared to the non-responders (n = 30). The retention rate at 54 weeks was also significantly higher in the REMIQ-positive group versus the negative group. After 14 weeks, more patients in the REMIQ-negative group were considered inadequate responders, and their infliximab doses were escalated. At baseline, the REMIQ-positive group had significantly lower C-reactive protein (CRP) levels compared to the negative group. Cox regression analysis with multiple variables showed that the positivity of REMIQ (hazard ratio [HR] 2.10 and 95% confidence interval [CI]: 1.55–5.71) at baseline was associated with the achievement of low disease activity. The positivities of rheumatoid factor and anti-CCP antibody at baseline were associated with the achievement of remission with infliximab treatment (HR 0.44, 95% CI: 0.09–0.82 and HR 0.35, 95% CI: 0.04–0.48, respectively). Conclusions: The results of this study suggest that the control of RA disease activity may be facilitated by using the REMIQ kit at 14 weeks to check whether it is necessary to increase a patient’s infliximab dose to ensure a therapeutic blood concentration that will help the patient achieve low disease activity.