Grain corn production is a relatively new sector in Malaysia. In this sector, a mobile dryer is utilized to reduce grain moisture content from approximately 25% to 14%. This study was undertaken to compare the drying performance between medium-sized (3 tonnes) and large-sized (7 tonnes) mobile dryers that are typically employed by local grain corn producers. In specific, this study examined the effect of drying time on fuel consumption and moisture reduction at three different drying temperatures; 60, 70 and 80°C, utilizing these dryers. The medium-sized mobile dryer consumed 43.6, 30.3 and 24.1 L/t of fuel to dry the grain at temperatures of 60, 70 and 80°C, respectively. The large-sized mobile dryer consumed 36.6, 34.9 and 31.7 L/t of fuel at drying temperatures of 60, 70 and 80°C, respectively. At the specified drying temperatures, the large-sized mobile dryer took 13.1, 11 and 9.1 hr to dry the grain. In addition, the results shows that the optimal drying temperature for both dryers was 80°C. The large-sized mobile dryer utilized 24% more fuel than the medium-sized mobile dryer to dry one tonne of grain. In terms of drying time, the large-sized mobile dryer required 55% longer time to finish each batch of grain drying than the medium-sized mobile dryer. It may be deduced that the medium-sized mobile dryer is more cost effective than the large-sized mobile dryer for in-field grain drying.