The effect of sample geometry aspect ratio (l/w) on the giant magnetoimpedance (GMI) in Fe67Co18Si11B4 amorphous ribbons was investigated systematically.The GMI profiles were measured as a function of the external magnetic field at different frequencies up to 110 MHz.The results show that there exists a critical aspect ratio ((l/w)0 =5.4) below which the maximum GMI effect and sensitivity ηdecrease with decreasingl/w and above which the maximum GMI effect keeps almost constant and ηdecreases with increasingl/w.The observed dependence on aspect ratio as (l/w) ＜ (l/w)o is correlated with the magnetization process:Complex domain structures emerged near the ribbon ends to decrease the magnetostatic energy,modify the transverse permeability and consequently GMI response.Contributions from transverse permeability and resistance may dominantly determine the change of GMI effect as (l/w) ＞ (l/w)0.