The cytoplasmic adaptor protein SLP‐65 (BLNK or BASH) is a cricital downstream effector of the B cell antigen receptor (BCR). Tyrosine‐phosphorylated SLP‐65 assembles intracellular signaling complexes such as the Ca^2 + initiation complex encompassing phospholipase C‐γ2 and Bruton′s tyrosine kinase. It is, however, unclear how the SLP‐65 signaling module can be recruited to the plasma membrane. Here we show that following B cell stimulation, SLP‐65 associates directly with the BCR signaling subunit, the Ig‐α / Ig‐β heterodimer. The interaction is mediated by theSrc homology 2 domain of SLP‐65 and the phosphorylated Ig‐α tyrosine 204, which is located outside of the immunoreceptor tyrosine‐based activation motif. Our data identify an unexpected BCR phosphorylation pattern and indicate that Ig‐α has the capability to serve as transmembrane adaptor in BCR signaling.