Background: Common carotid artery intima-media thickness (cIMT) has been associated with cardiovascular diseases, including stroke and coronary heart disease. There is a limited number of studies that specifically address the variability of ultrasound imaging modes in measuring cIMT. Therefore, this study aimed to assess the agreement-level and inter-observer reproducibility of cIMT measurements using B-mode and M-mode. Materials and Methods: B-mode and M-mode ultrasound imaging were used in measuring cIMT of healthy subjects using linear-array transducer. Inter-imaging mode agreement and inter-observer reproducibility of B-mode and M-mode were assessed using Intraclass correlation coefficient (ICC). Differences in cIMT measurements between imaging modes and observers were determined using paired t-test Results: There was significant difference between B-mode and M-mode in measuring cIMT (mean difference (MD), 0.03 mm, 95% CI 0.02 - 0.05, p<0.001).  Intra-imaging mode agreement was poor with ICC of 0.39. Inter-observer reproducibility of cIMT measured using B-mode and M-mode were good and moderate, respectively, (B-mode ICC of 0.76, 95% CI 0.64 - 0.84, p<0.01; M-mode ICC of 0.68, 95% CI 0.52 - 0.78, p<0.01). No significant difference between the two observers in measuring cIMT measured using B-mode or M-mode (B-mode p=0.3; M-mode p=0.4).  Conclusion: There was a significant difference and poor intra-imaging mode agreement between B-mode and M-mode in measuring cIMT. B-mode showed higher inter-observer reproducibility of cIMT measurement than M-mode. Further studies investigating the variability and agreement between ultrasound imaging modes of patients with thickened cIMT are required.