Methyl nitrite (MN) is identified in the exhaust gases of methanol-fueled vehicles as one of the trace components. However, for a high concentration of methanol at low temperatures, as occurs in start-up conditions, more MN would be emitted due to reaction with the co-exhaust emission of nitrogen dioxide (NO2). In this study, the concentration of MN in the exhaust emission of a methanol-fueled truck was measured during cold start-up. To prevent the secondary formation of MN during the measurement procedure, the best method is thought to be dilution of the sample with hot clean air. Also NO2 measurement methods, including those for high-MN-concentration samples, were studied. The behavior of MN emission is similar to that of other pollutants. The highest concentration occurs about 80 (s) after the engine starts, and MN is never detected after 180 (s). At low temperatures(-5∼5°C), the MN level was more than 5 times higher than that under warm temperature conditions (20°C). It was demonstrated that some NO2 emitted from the engine was converted into MN by the catalyst converter system.