Epidermal growth factor receptor (EGFR) was functionally reconstituted into liposome membrane. Triton X-100 was removed by Bio-beads SM-2, More than 80% of the reconstituted EGFR possessed right-side-out orientation with the EGF binding side facing the medium. The tyrosine kinase assay of the EG;FR was carried out in the presence of the antibiotic alamethicin, The reconstituted EGFR tyrosine kinase was well activated by EGF. The influence of lipid composition on tyrosine kinase activity was investigated, Introduction of cholesterol into the dioleoylphophatidylcholine (DOPC) liposome membrane resulted in the decrease of tyrosine kinase activity. The tyrosine kinase activity of EGFR in distearylphosphatidylcholine liposome was much lower than that of EGFR-DOPC proteoliposome, Results indicated the importance of membrane fluidity on the apparent tyrosine kinase activity of reconstituted EGFR.