AIM: To compare the differences and agreement of ocular biometric parameters in highly myopic eyes obtained by optical biometric measurement instruments, the OA-2000 and IOLMaster 500. METHODS: Totally, 90 patients (90 eyes) were included. They were divided into high myopia group and control group. Ocular parameters, including axial length (AL), mean keratometry (Km), anterior chamber depth (ACD), and white to white (WTW), were obtained from the OA-2000 and IOLMaster 500. RESULTS: For the control group, we applied Bland-Altman graphs to assess the 95% limits of agreement (LoA) for most parameters including AL, ACD, Km, and WTW (-0.24 to 0.29 mm, -0.22 to 0.45 mm, -0.39 to 0.31 D, and -0.90 to 0.86 mm, respectively). In high myopia patients, AL, ACD, Km values had wider 95% LoA (-0.34 to 0.32 mm, -0.36 to 0.34 mm, -0.57 to 0.47 D, respectively), except WTW (-0.80 to 0.68 mm). Differences were not statistically significant between these two instruments (P>0.05). CONCLUSION: Most parameters obtained by the OA-2000 and IOLMaster 500 are comparable, including the AL, ACD, and K values. Among them, the agreement of the high myopia patients is poor compared to the patients without high myopia.