Transport of weaned pigs poses special challenges because of their size and thermal needs as well as the extended distances and transport times. The resultant economic impact can be substantial. Compared to transport of market pigs, weaned pigs generally encounter much farther travel distances with different adapting abilities to the environmental conditions. The objectives of this study were: 1) to characterize the environmental conditions within a typical transport trailer for weaned piglets to determine if current management practices and trailer design provides an acceptable environment as evidenced by mortality rates and environmental parameters, and 2) to analyze airflow patterns of the tranport trailer using a scale model in a wind tunnel. Data from 78 usable transport trips were collected for air temperature in each trailer compartment, ambient temperature,distance traveled, time traveled, stocking density, and mortality by compartment. The 78 trips had an average distance of 778 km (range of 264 to 1016 km), travel time of 8.51 h (range of 3.4 to 12.3 h), and mortality rate of 0.031% (range of 0 to 1.11%). There was no significant difference in mortality by compartment (p>0.05). The results indicate that if pigs are transported at a higher stocking density, the compartment temperatures would be similar during cold weather (e.g., 2°C). Under mild weather condition (e.g., 16°C), significant differences could exist in compartment temperature between part of the upper deck (Upper 1) and the lower deck (Lower 4) (p<0.05). In comparison, no significant differences were found at warm conditions (e.g., 29°C) (p>0.05). In addition to the weather influence, in-trailer environment is affected by the side openings which may be adjusted by the driver.