In this paper using δ-quasi-monotone sequences a theorem on\(\left| {\bar N,p_n ;\delta } \right|_k \) summability factors of infinite series, which generalizes a theorem of Bor [4] on\(\left| {\bar N,p_n } \right|_k \) summability factors of infinite series, is proved. Also, in the special case this theorem includes a result of Mazhar [8] on |C, 1|k summability factors.