In designing land based structures and offshore structures, as well as ships including LNG carriers, it is very important to accurately predict the buckling strength and collapse strength of axially compressed cylinders, especially with initial imperfections. Many researches have been reported with respect to the elastic buckling strength of initially imperfect long cylinders, but few have been made of the buckling strength of initially imperfect short cylinders such as tank skirts of Moss-type LNG carriers, especially in the plastic range. This paper investigates effects of the initial imperfections on the collapse strength of axially compressed short cylinders, utilizing the finite element method (FEM). Main conclusions obtained from this study are as follows : (1) Effects of initial imperfections on the buckling strength of short cylinders, not only in the elastic range but also in the plastic range, have been presented. (2) It is important to precisely calculate pre-buckling deformations of short cylinders even if they are in the elastic range, since the non-linear behavior would greatly affect the buckling strength. (3) When cylinders collapse by axially compressed forces in the plastic range, the extent of their plasticity may be expressed by parameter( R σ _y ) /( tE ). (4) In the plastic range, the outer initially imperfect cylinders give lower buckling load than the inner ones. This is contrary to the case of elastic buckling. Further, in the plastic range, the cylinders with Batdorf parameter Z =14 are most sensitive to the initial imperfections.