The X-H insertion reaction constitutes a powerful tool to create diversity through diazo decomposition of diazocarbonyl compounds. However, until now, the X-H insertion on α-diazo-β-aryl-β-hydroxyester scaffolds, readily prepared by aldol-type addition, remained a challenge for the organic chemist. We report herein the first O-H insertions on O-protected α-diazo-β-aryl-β-hydroxyesters, providing a straightforward access to a wide range of α,β-dioxygenated esters through modulation of the alcohol and of the aryl substituent. The key feature to achieve this transformation is the use of Rh(I) catalysts, which proved crucial to favor the targeted O-H insertion product over the competing 1,2-H and 1,2-Ar migration products. Overall, 31 O-H insertion products have been prepared, in moderate to good yields, with diastereoisomeric ratio up to 7.5:1 in favor of the syn diastereoisomer.