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In the cities of the U.S. the worsening ozone problem has attracted attention and prompted reinforcement of regulations against emissions of hydrocarbons (HC) from automobiles. To cope with this situation, a reduction of HC is a vital challenge for the automotive industry. HC emission comes mainly from a cold engine, which usually uses a richer air-fuel mixture to achieve stable combustion and secure good driveability. The purpose of this paper is to show that using a engine with variable valv1e timing and lift system (VTEC) (1)∼(2) it is possible to reduce considerably HC emission in cold-start conditions. In other words, it is able to employ a leaner mixture than in existing engines (A/F=15.5) by using the VTEC system to alter the valve timing and lift according to various driving conditions, thereby considerably reducing HC emissions due to the improvement and stabilization of engine combustion.