Hydrophobically modified anion polyelectrolytes based on Fenugreek gum（HmCmFG）were prepared by fixation of dodecyl（Dod）or cetyl（Cet）chains onto carboxymethyl Fenugreek gum backbone via ester functions.Fluorescence excitation and emission spectra of probe pyrene and UV spectra were used to investigate the hydrophobically associating behavior of HmCmFG in solutions.The experiment data showed that hydrophobically associating behavior was significantly affected by the length and substitution degree of alkyl chains and concentration of low molecular electrolyte NaCl，the increase of which was in favor of the formation of hydrophobic microdomains.Viscometric experiments were carried out to study the interactions between HmCmFG and NaCl，〖HJ〗hexadecyl trimethyl ammonium bromide（CTAB）or sodium dodecyl sulfate（SDS）.The addition of NaCl mainly strengthened intermolecular hydrophobic interactions for HmCmFG with the substitution degree of dodecyl lower than 5.7，leading to increasing viscosity of solutions.The effect of CTAB on the viscosity of solutions of HmCmFG with dodecyl substitution degree lower than 5.7 was greater than that of SDS.As for Dod 10.2 and Cet 6.3，the addition of NaCl，CTAB or SDS decreased solution viscosities by strengthening intra-molecular hydrophobic aggregation.