Six reverse‐transcription loop‐mediated isothermal amplification (RT‐LAMP) primers designed against conserved regions of segment 6 (s6) gene were used for the detection of grass carp Ctenopharyngodon idella reovirus (GCRV) HZ08 subtype. The entire amplification could be completed within 40 min at 62·3° C. The RT‐LAMP showed higher sensitivity than reverse‐transcription polymerase chain reaction (RT‐PCR). The RNA detection limit was 10 copies µl−1 for RT‐LAMP assay and 100 copies µl−1 for conventional RT‐PCR. In specificity tests, no cross‐reactivity was detected in other viruses from common aquatic animals. In addition, the reaction results can be visualized by using calcein fluorescent dye. Furthermore, a total of 86 samples were tested by RT‐LAMP, RT‐PCR and virus isolation. The results demonstrated that all 54 specimens identified as positive by virus isolation were also positive when detected by RT‐LAMP. Seven out of 54 samples, however, were misidentified by RT‐PCR. The RT‐LAMP method is more accurate than conventional RT‐PCR. The results indicate that RT‐LAMP has potential as a simple and rapid diagnosis technique for the detection of GCRV HZ08 subtype infection.