We performed an optical spectroscopic monitoring of the blazar 3C 454.3 from September 2003 to July 2008. Sixteen optical spectra were obtained during different runs, which constitute the first spectroscopic monitoring done in the rest-frame UV region (z=0.859). An overall flux variation of the MgH(λ2800 A) by a factor ～ 3 was observed, while the corresponding UV continuum (Fcont at λ3000 A) changed by a factor 14. The MgII emission lines respond propor-tionally to the continuum variations when the source is in a low-activity state. In contrast, near the optical outbursts detected in 2005 and 2007, the MgII emission lines showed little response to the continuum flux variations. During the monitored period the UV Fell Hux changed by a factor ～ 6 and correlated with Fcont, (Υ= 0.92). A negative correlation between. EW(Mg II) and Fcont was found, i.e. the so-called "Intrinsic Baldwin Effect".
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