The catalysis of a silica-supported chromium system {Cr[CH(SiMe3)(2)](3)/ SiO(2)J was compared with a silica-supported chromium oxide catalyst, the Phillips catalyst (CrO2/SiO2). This catalyst was prepared by the calcining of the typical silica support used for the Phillips catalyst at 600 degreesC and by the support of tris[bis(trimethylsilyl)methyllchromium(III) {Cr[CH(SiMe3)(2)](3)} on the silica. In the slurry-phase polymerization, this catalyst conducted the polymerization of ethylene at a high activity without organoaluminum. compounds as cocatalysts or scavengers. The activity per Cr was about 6-7 times higher than that of the Phillips catalyst. Upon the introduction of hydrogen to the system, the molecular weight of polyethylene did not change with the Phillips catalyst, but it decreased with the Cr[CH(SiMe3)(2)](3)/SiO2 catalyst.