The objective of this study was, using the data of field experiment and visualization of internal airflow,to clearly understand forced ventilation of a piglet house with perforated ceiling which was very popular in Korea. This study was conducted at a commercial piglet house to investigate the performance of the forced ventilation and determine the effect of the ventilation system on internal airflow, air temperature, humidity, dust, and gas in the piglet house. The internal airflow patterns were studied with the help of computational fluid dynamics (CFD). Comparing the recommended maximum ventilation rate and measured ventilation rate, the ventilation system of the piglet house was 16% overestimated. The air temperature measured at 0.8 m from the floor in a compartment of the piglet house was always higher than the setting temperature while relative humidity, dust, and ammonia gas were controlled pretty well during data collection. Compared to the measured air velocities at piglet location in the compartment, the CFD computed results showed 10-18% error. The CFD computed results without piglets showed that the maximum air velocities at piglet location were 0.06, 0.55, and 0.95 m/s, respectively for 5, 50, and 100% of ventilation settings. Observing the dilution of internal relative humidity of the time-dependent CFD model, very poor environmental conditions were found at both end wall areas compared to the other areas of the compartment.