摘要： For any ring R (probably without identity), some new characterizations of weak symmetric rings are given. It is proved that R is weak symmetric if and only if every left ideal generated by a nilpotent element is nil. It's shown that direct products of weak symmetric rings need not be weak symmetric. As applications, some new characterizations of quasi-duo rings, NI rings and clean rings are given. It is proved that R is an NI ring if and only if R is weak symmetric and R satisfies the Ko?the's conjecture.