The protected oligophosphoseryl peptides from bovine caseins, Z‐Xxx‐{Ser[PO(OPh)2]}3‐Glu(OBzl)‐OBzl for Xxx = Ile, Val, Gly, Leu and Ph = phenyl, were synthesized in high yields by stepwise lengthening using Boc‐Ser[PO(OPh)2]‐OH as acylating carboxyl component andN‐ethyl‐N′‐(3‐dimethylaminopropyl)‐carbodiimide hydrochloride as coupling reagent. The hydrogenolytic deprotection (PtO2) was carried out with the valine derivative and with the tetrapeptide Ser[PO(OPh)2]3‐Glu(OBzl)‐OBzl. Phosphorylation of oligoseryl peptides failed to give the expected products. Large scale phosphorylation of protected serine was carried out in the presence of triethylamine using absolute ether as a solvent. 2,2,2‐Trichloroethyl group (Tc) was shown to be a useful phosphorus protecting moiety in phosphopeptide synthesis: Boc‐Ser[PO(OTc)2]‐OBzl, Z‐Ser[PO(OTc)2]‐OBzl and Boc‐Glu(OBzl)‐Ser[PO(OTc)2]‐OBzl were synthesized in high yields using b