Disclosed are a silicon-containing cerium composite
oxide which is capable of maintaining a large specific
surface area even used in a high temperature environment,
and which has excellent heat resistance and reducibility,
as well as a method for producing the composite oxide and
a catalyst for exhaust gas purification employing the
composite oxide. The composite oxide contains 2 to 2 0 mas s%
silicon in terms of S102, has properties of exhibiting a
specific surface area of not less than 40 m2/g as measured
by the BET method after calcination at 1000 °C for 5 hours,
and a reducibility of not lower than 30 % as calculated
from measurement of temperature-programmed reduction from
50 00 to 900 °C after calcination at 1000 00 for 5 hours,
and is suitable for a co-catalyst for a catalyst for exhaust
gas purification.