The temperature dependence of the magnetic susceptibility, χ(T ), is investigated for one-dimensional interacting electron systems at quarter-filling within the Kadanoff-Wilson renormalization-group method. The forward scattering on the same branch (the g4-process) is examined together with the backward (g1) and forward (g2) scattering amplitudes on opposite branches. In connection with lattice models, we show that χ(T ) is strongly enhanced by the nearest-neighbor interaction, an enhancement that surpasses one of the next-nearest-neighbor interaction. A connection between our predictions for χ(T ) and experimental results for χ(T ) in quasi-one-dimensional organic conductors is presented.KEYWORDS: magnetic susceptibility, renormalization group, long-range Coulomb interaction, extendedHubbard model, quarter-filling, one-dimension, (TMTTF)2X, (TMTSF)2XIn low dimensional conductors, the influence of longrange Coulomb interactions, or the off-site interaction V 's are known to lead to various interesting ordered states, such as charge ordering 1 and spin-density wave (SDW) state coexisting with charge-density wave (CDW).2, 3 At the present stage, however, the effect of V 's is not clearly understood compared with that of the on-site repulsion U . The purpose of this letter is to analyze the effect of V 's on the quasi-one-dimensional conductor in the normal state by calculating the temperature dependence of the magnetic susceptibility χ(T ) for the one-dimensional system at quarter-filling. The results shed some light on the magnetic properties of both normal and ordered states in these kinds of materials.A lot of studies of χ(T ) were devoted to the onedimensional (1D) Hubbard model, i.e., for V 's = 0. The Bethe ansatz gives us an exact solution, but χ only at T = 0 is available for the 1D Hubbard model. 4 The temperature dependence of χ can be extracted from numerical simulations but only at high temperatures.5 For U smaller than the bandwidth, the renormalization-group (RG) approach gives results that quantitatively agree with both the exact solution at T = 0 and the numerical solutions at high temperatures.5 In the presence of V 's, however, there is no exact solution, and the size of numerical simulations becomes exceedingly large. These techniques are then of limited use to investigate the effect of V 's.In this letter, we use the RG technique to calculate χ(T ) for the full temperature range from zero to the bandwidth E 0 in the presence of V 's (> 0). Considering the possible interactions for branches of right and left going electrons in the continuum limit, we take into account the forward scattering on the same branch (SB), denoted as the g 4 -process, with the backward (g 1 ) and forward (g 2 ) scattering processes on opposite branches. This is the first derivation of the RG flows of the sets of coupling constants and χ(T ) at the one-loop level in- * E-mail address: fuseya@slab.phys.nagoya-u.ac.jp.cluding the non-logarithmic channels for particles on the SB, which become important at finite-temperature...