University of Tehran Journal of Sciences, Islamic Republic of Iran 1016-1104 18 1 2007 03 01 - - 30996 EN Journal Article This paper is concerned with the problem of finding a lower bound for certain matrix operators such as Hausdorff and Hilbert matrices on sequence spaces lp(w) and Lorentz sequence spaces d(w,p), which is recently considered in [7,8], similar to [13] considered by J. Pecaric, I. Peric and R. Roki. Also, this study is an extension of some works which are studied before in [1,2,7,8]. https://jsciences.ut.ac.ir/article_30996_3277651248e7ccf4b6e6a8b1763508fe.pdf