Summary1. The hypotensive effect of cross‐fostering in spontaneously hypertensive rats (SHR) is thought to involve adjustments in renal function. However, its association with renal anti‐oxidant/oxidant balance during cross‐fostering is not known.2. The present study examined the effect of cross‐fostering and in‐fostering of 1‐day‐old offspring between SHR and Wistar‐Kyoto (WKY) dams on renal anti‐oxidant/oxidant status and systolic blood pressure (SBP). Renal anti‐oxidant/oxidant status and SBP were determined in the offspring from 4–16 weeks of age.3. Cross‐fostered SHR had significantly lower SBP than in‐fostered SHR at 6, 8 and 12 weeks, but not at 16 weeks (127 ± 1 vs 144 ± 2, 138 ± 1 vs 160 ± 1, 174 ± 2 vs 184 ± 2 and 199 ± 2 vs 194 ± 3 mmHg at 6, 8, 12 and 16 weeks, respectively). No differences in SBP were evident between cross‐fostered and in‐fostered WKY rats. There were no significant differences in levels of thiobarbituric acid‐reactive substances (TBARS), protein carbonyl and total anti‐oxidant status (TAS) or superoxide dismutase, catalase, glutathione peroxidase (GPx), glutathione S‐transferase and glutathione reductase activity between cross‐fostered and in‐fostered SHR or WKY offspring. However, compared with WKY rats, catalase activity was higher at 6 and 16 weeks, TAS was higher at 16 weeks and GPx activity and TBARS were lower at 16 weeks in SHR.4. It appears that cross‐fostering of SHR offspring to WKY dams during the early postnatal period causes a transient delay in the rise in blood pressure in SHR and that this does not involve the renal anti‐oxidant/oxidant system.