Shape-selective methylation of toluene (T) with methanol (M) was carried out in a continuous flow fixed-bed reactor over modified HZSM-5 catalysts. The effect of metal modification on the catalytic performance, especially the catalyst stability, was investigated. Various techniques including X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM), were used to characterize the catalysts. The results showed that P-Mg modified catalysts with 3 wt% SiO(2) exhibited excellent stability (more than 500 h), but lowered p-xylene selectivity (less than 90%). Upon further increasing the amount of SiO(2), the catalyst deactivated in a relatively short time on stream, although the para-selectivity was significantly increased up to 99.5%. The high p-xylene-selectivity catalyst modified further with Pt, Pd, Co, Ni metal demonstrated excellent stability, even after 100-400 h on stream, and the selectivity for p-xylene of more than 98.3% with toluene conversion of 20.0% was achieved. Hence, loading metals with good hydrogenation properties, such as Pt, Pd, Co and Ni, was an effective method to improve the catalyst stability. (C) 2010 Elsevier B.V. All rights reserved.