In the present study we have investigated the effect of increased serine/threonine phosphorylation of insulin receptor substrates‐1 and ‐2 (IRS‐1 and IRS‐2) by okadaic acid pretreatment on brown adipocyte insulin signalling leading to glucose transport, an important metabolic effect of insulin in brown adipose tissue. Okadaic acid pretreatment before insulin stimulation decreased IRS‐1 and IRS‐2 tyrosine phosphorylation in parallel to a decrease in their sodium dodecyl sulfate–polyacrylamide gel electrophoresis mobility. IRS‐1/IRS‐2‐associated p85α and phosphatidylinositol (PI) 3‐kinase enzymatic activity were partly reduced in brown adipocytes pretreated with okadaic acid upon stimulation with insulin. Furthermore, insulin‐induced glucose uptake was totally abolished by the inhibitor in parallel with a total inhibition of insulin‐induced protein kinase C (PKC) ζ activity. However, activation of Akt/PKB or p70 S6 kinase (p70s6k) by insulin remained unaltered. Our results suggest that downstream of PI 3‐kinase, insulin signalling diverges into at least two independent pathways through Akt/PKB and PKC ζ, the PKC ζ pathway contributing to glucose transport induced by insulin in fetal brown adipocytes.