Oxidative stress is a potential mechanism involved in the pathogenesis of iron deficiency anaemia (IDA). Although a tendency for hypercoagulability has been reported in IDA, its underlying mechanism is yet to be elucidated. This study investigated the probable relationship between oxidative stress and hypercoagulability in children with IDA. This study included 57 children diagnosed with IDA (IDA group) between October 2016 and October 2017 in addition to 48 healthy children (control group). The maximum clot firmness (MCF) index, and clot formation time (CFT) index, which are indicators of hypercoagulability in rotational thromboelastometry assays [intrinsic TEM (INTEM) and extrinsic TEM (EXTEM)] derived from our previous study, were recorded. Total oxidant status (TOS), total antioxidant capacity (TAC) and oxidative stress index (OSI) were analysed from serum samples of the individuals. In IDA group, OSI and TOS levels were higher and TAC level was lower compared to the control group (P<0.001, for all). The EXTEM and INTEM MCF in the IDA group was higher than in the control group, while the INTEM CFT was lower than in the control group (P<0.001, P<0.001, P<0.05, published data). TOS and OSI had a negative correlation with INTEM CFT (r:-0.361, P<0.001 and r:-0.333, P=0.001) and a positive correlation with INTEM MCF (r:+0.420, P<0.001 and r:+0.367, P<0.001) and EXTEM MCF (r:+0.476, P<0.001 and r:+0.403, P<0.001). However, TAC demonstrated no correlation with CFT and MCF index. The oxidant-antioxidant balance is disrupted in favour of oxidative stress in children with IDA. In addition, TOS and OSI, which are parameters of oxidative stress, are correlated with CFT and MCF indices. Oxidative stress appears to be an important factor for the development of tendency to hypercoagulability in IDA. Copyright (C) 2021 Wolters Kluwer Health, Inc. All rights reserved.