[Claim 1]
A polyolefin microporous membrane having the following properties (1) to (5):
(1) tensile strength (MPa) and tensile elongation (%) in
MD and TD satisfy the following equation (I):
[{(tensile strength in MD) x (tensile elongation in MD)
/ 100}2 + {(tensile strength in TD) x (tensile elongation in TD)
/ 100}2]1/2 > 300 Relation (I) ;
(2) tensile strength in MD and TD is at least 196 MPa;
(3) maximum pore diameter measured by a perm porometer is up to 6 0 nm;
(4 ) average flow pore diameter measured by a perm porometer is up to 4 0 nm; and
(5) porosity is at least 40%.
[Claim 2]
A polyolefin microporous membrane according to claim 1 having the following property (6):
(6) ratio of the tensile strength in MD to the tensile
strength in TD (the tensile strength in MD / the tensile strength
in TD) is at least 0.8 to up to 1.2.
[Claim 3]
A polyolefin microporous membrane according to claim 1 or 2 having the following property (7):
(7) ratio of the tensile elongation in MD to the tensile
elongation in TD (the tensile elongation in MD / the tensile
elongation in TD) is at least 0.75 to up to 1.25.
[Claim 4]
A polyolefin microporous membrane according to any one of claims 1 to 3 having the following property (8):
(8) the tensile elongation in MD and the tensile elongation
in TD are respectively at least 90%.
[Claim 5]
A polyolefin microporous membrane according to any one of claims 1 to 4 wherein the membrane thickness is up to 2 0 urn. [Claim 6]

A polyolef in microporous membrane according to any one of claims 1 to 5 wherein the membrane has a puncture strength converted to the membrane thickness of 12 |j,m of at least 5 N. [Claim 7]
A polyolef in microporous membrane according to any one of
claims 1 to 5 wherein the tensile strength (MPa) and the tensile
elongation (%) in MD and TD satisfy the following relation (II) :
[{(tensile strength in MD) x (tensile elongation in MD)
/ 100}2 + { (tensile strength in TD) x (tensile elongation in TD)
/ 100}2]1/2 > 350 (II) .
[Claim 8]
A separator for secondary battery with nonaqueous electrolyte prepared by using the polyolefin microporous membrane according to any one of claims 1 to 7. [Claim 9]
A separator for secondary battery with nonaqueous electrolyte according to claim 8 wherein the separator has a coating layer containing inorganic particles and a binder resin at least on one surface. [Claim 10]
A secondary battery with nonaqueous electrolyte including the separator for secondary battery with nonaqueous electrolyte according to claim 8 or 9.