Laying hen production plays an important role in particulate matter (PM) emissions which potentially cause air pollution and adverse health effect on animals and workers. Aviary cage-free (CF) egg production systems have been attracting increasing attention due to concerns over animal welfare and increased market demand. While studies have been conducted to characterize PM concentrations and emissions of aviary CF houses with litter floor, few reports are available of this information for aviary CF layer houses equipped with slat floor. In this study, PM concentrations – both spatial and diurnal patters inside a pilot-scale aviary CF layer house (1,800 laying hens, LxWxH of 28.2 x 9.0 x 3.0 m) in northern China were measured under winter conditions. Daily mean PM2.5, PM10, and TSP levels were found to be 0.19±0.11, 1.05±0.65, 2.90±2.07 mg/m3, respectively, which were considerably lower than those reported in previous studies of aviary CF houses with litter floor in cold weather. Daytime PM concentrations were significantly higher than those at night primarily due to differences in animal activity and feed supply. The average PM10 and TSP concentrations during light period (5:00-21:00 h) were 1.34 mg/m3 and 3.75 mg/m3, amounting to 279% and 304% of those during the dark period (21:00-5:00h), respectively. Spatial variations for PM10 and TSP were observed in the experimental hen house due to non-uniform distribution of ventilation air and localized generation of the constituents. Higher TSP concentrations (4.26 mg/m3) were found at worker respiratory level (2.0 m) as compared to floor level (0.5 m, 3.00 mg/m3). TSP concentration at one end of the house (west) was found to be 28.3% and 86.9% higher than the middle and the opposite (east) end. This spatial variation characteristic points out the importance of multi-location sampling when assessing indoor air quality and aerial emissions (for cross ventilation). Data from this study will be useful for future improvement of the housing ventilation design and operation. Future study should also assess PM concentrations of the housing style under warm seasons.