Antimicrobial resistance (AMR) is a threat to animal and human health globally. Antimicrobials are used in aquaculture to control different bacterial diseases. However, inappropriate use of antimicrobials can accelerate the emergence of AMR. This study was conducted to determine antimicrobial resistance in Streptococcus agalactiae, which affects and causes diseases with high mortality in tilapia. A total of 26 S. agalactiae isolates were streaked from kidney/brain/liver samples of diseased farmed tilapia from 2017 to 2021 at Hai Duong, Bac Ninh, Hoa Binh, Yen Bai provinces. The sensitivity of the isolates to 7 antimicrobials was established by disc diffusion (Oxiod). The results showed that levels of resistance vary from S. agalactiae to DOX (34.4%), RIF (64.1%), TET (45.0%), ERY (64.8%), TMP-SMX (70%), FLO (35.3%), and AMP (75%). The resistance rate to DOX was significantly different (p<0.05) compared to ERY. S. agalactiae has the highest resistance to 2 types of antibiotics at 19.2%, followed by resistance to 3 types (15.4%), and resistance to 6 and 7 types of antibiotics at a rate of 11.5%. The resistance in 1 type, 4 types, and 5 types of antibiotics was observed lowest at 7.7%. Vietnamese tilapia farmers need guidelines for effective antimicrobial treatment and wwider take up of vaccine or sustainable farming technology to prevent infections caused by S. agalactiae and reduce emergence of AMR.