The objective of this study was to determine the relationships between luteal size (LS), progesterone (P4), and luteal blood flow (LBF) during the first 3 wk after insemination in pregnant and non-pregnant Bos indicus dairy cows. Lactating cows (n = 13) of mixed parity that were exhibiting normal estrous cyclicity were enrolled in the study. Estrus detection was carried out twice daily to determine the onset of standing heat (d 0). All cows were artificially inseminated and were classified as pregnant (n = 8) or non-pregnant (n = 5). To compare the LS and LBF after AI, B-mode and color Doppler sonography of ovaries were performed on d 4, 5, 6, 7 (luteal growth phase; LGP), 8, 10, 12, 14, 16, (luteal static phase; LSP), in pregnant and non-pregnant cows. In addition, non-pregnant cows were also examined on d 17, 18, 19, 20, 21 (luteal regression phase; LRP). The corpus luteum (CL) size was measured by taking 3 cross sectional images with maximum areas of the CL. Blood samples from the jugular vein were collected after each sonographic examination for measurement of P4. The mean values and relationships between LS, concentrations of P4, and LBF were subjected to ANOVA of repeated measurements using the PROC GLIMMIX procedure and Pearson correlation coefficient, respectively. Results revealed that the mean LS, concentrations of P4, and LBF increased significantly (P < 0.05) every day during the LGP. Mean LS, P4, and LBF showed highest values (P < 0.05) during the LSP and then declined (P < 0.05) abruptly in the LRP in non-pregnant cows. In pregnant cows, the mean LS, P4, and LBF increased also linearly (P < 0.05) during the LGP and LSP that remained elevated thereafter. A positive correlation (r = 0.95; P < 0.05) existed between LS and concentrations of P4; and equally strong correlation (r = 0.96; P < 0.05) was observed between LBF and P4 during d 4 to 21 in pregnant cows. In conclusion, the present study has provided new information about relationships between LS, P4, and LBF during the first 3 wk after AI in pregnant and non-pregnant Bos indicus dairy cows.