Ambient temperature change is one of the risk factors of human health. Moreover, links between white blood cell counts (WBC) and diseases have been revealed in the literature. Still, we do not know of any association between ambient temperature change and WBC counts. The aim of our study is to investigate the relationship between ambient temperature change and WBC counts. We conducted this two-year population-based observational study in Kaohsiung city, recruiting voluntary community participants. Total WBC and differential counts, demographic data and health hazard habits were collected and matched with the meteorological data of air-quality monitoring stations with participants’ study dates and addresses. Generalized additive models (GAM) with penalized smoothing spline functions were performed for the trend of temperature changes and WBC counts. There were 9278 participants (45.3% male, aged 54.3 ± 5.9 years-old) included in analysis. Compared with stable weather conditions, the WBC counts were statistically higher when the one-day lag temperature changed over 2 degrees Celsius, regardless of whether colder or hotter. We found a V-shaped pattern association between WBC counts and temperature changes in GAM. The ambient temperature change was associated with WBC counts, and might imply an impact on systematic inflammation response.