Urban park patronage is intimately linked to the thermal comfort level perceived by visitors. This study quantified the effects of nine park-design and urban-landscape parameters on air temperature and relative humidity in summer by deploying 100 sensors in 14 urban parks in Hong Kong. The field data were compared with a reference weather station and analysed with multiple regression. The sampled parks were on average 0.2 °C warmer and 1.7% less humid than the reference. A notable temperature reduction (mean = 0.6 °C and max. = 4.9 °C) was only observed in the largest park in Hong Kong. The daily variations in cooling and humidifying magnitudes were strongly dependent on background temperature. The distance from sea, shrub cover, tree cover and sky view factor were significant parameters that controlled temperature and relative humidity. Mean temperature could be predicted to cool by 0.6 °C if the park was 1 km closer to the sea. For every 10% increase in shrub and tree covers, mean temperature would drop by 0.07 and 0.04 °C respectively. Larger parks with good coverage of woody vegetation should be developed to improve urban microclimate within parks and mediate the warming effect of nearby built-up areas.