The pandemic of COVID-19 continues with new variants. More than 401 million people in the world infected by COVID-19 and approximately 5.7 million people lost their lives. Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has respiratory system as a target. This virus uses a receptor binding domain of SARS-CoV-2 Spike (sRBD) protein to bind ACE-2 receptor and enter human respiratory cells. The antibody to sRBD protein will block the virus. Convalescent plasma from recovered COVID-19 patient contains neutralization antibody which can neutralize sRBD and eliminate the virus. Therefore, this study aims to assess the therapeutic effect of convalescent plasma to neutralization antibody and inflammatory parameter level in moderate COVID-19 patients. This is a one-group pretest-posttest study of nine moderate COVID-19 patients admitted in Unggul Karsa Medika Hospital, Bandung, Indonesia. The study was done from August 1, 2021 to January 1, 2022. The level of neutralization antibody and inflammatory parameter were assessed before and after convalescent plasma therapy in moderate COVID-19 patient. Data analysis performed by SPSS program with p < 0.05 and dependent t-test. Our study shows that convalescent plasma therapy can influence the increase of neutralization antibody (142. 5 AU/mL vs 13.432 AU/mL, p value = 0.011) and the decrease of Interleukin-6 (IL-6) (41.61 pg/mL vs 14.5 pg/mL, p value = 0.008) and C-reactive protein (CRP) level (84.2 mg/L vs 17.4 mg/L, p-value = 0.018) in moderate COVID-19 patient. The patients were also getting better clinically, with the use of oxygen decreasing gradually from non-rebreathing masks to nasal cannula and from nasal cannula to room air after given convalescent plasma therapy. Therefore, we conclude that convalescent plasma therapy has a positive role in increasing neutralization antibody and decreasing inflammatory parameters which are IL-6 and CRP, thus had potential usefulness in therapy for moderate COVID-19 patients.