This paper aims to examine the U.S. property casualty insurer’s organizational structure, corporate governance and loss reserve estimating in relation to actuaries switching. The results show that stock insurers are more likely to switch their actuaries than mutual insurers. Insurers with high percentage of long-tail business are also more likely to switch their actuaries. Large and weak financial condition insurers are less likely to switch their actuaries. We find that insurers with under-estimated (over-estimated) reserve error in the previous year are not significantly to switch their actuaries. In terms of corporate governance variables, the evidence shows that insurers with large board size are more likely to switch their actuaries from internal actuary to Big 6 actuarial firms, whereas insurers with CEO/Chairperson duality are more likely to switch their actuaries from Big 6 actuarial firms to internal actuary. We next examine the impact of organizational structure, corporate governance and actuaries switching on reserve error. The evidence shows that insurers tend to have less reserve error after actuaries switching than before. Insurers with CEO/Chairperson duality and high percentage of insider directors on the board are positively related to reserve error post actuaries switching. In addition, stock insurers are more likely to have less reserve error after actuaries switching from internal actuary to Big 6 actuarial firms than stock insurers without actuaries switching. Insurers with CEO/Chairperson duality and large board size are positively and significantly related to reserve error when actuaries switching from Big 6 actuarial firms to internal actuary. We also find that insurers with actuaries switching form internal actuary to Big 6 actuaries are more likely to have less under-estimate reserve error than insurers without actuaries switching. Examination of the impact of the Sarbanes-Oxley Act (SOX) on reserve error indicates that insurers are more likely to switch actuaries after SOX.