Objective To evaluate long-term trends of weather factors in Beijing. Methods Based on the observed data from Beijing between 1951 and 2012, the Mann-Kendall test and Sen's slope method were applied to detect and quantify the long-term trends of weather variables (eg, the maximum,minmum,and mean temperature, mean diurnal temperature, relative humidity, atmospheric pressure, sunshine duration and precipitation). Results The annual mean temperature rose significantly during 1951-2012 at the rate of 0.040 ℃/year. The most evident warming occurred in winter, and its mean temperature showed significant increasing at the rate of 0.050 ℃/year. The annual and seasonal mean diurnal temperature decreased significantly at rate of 0.034 ℃/year. Furthermore, annual mean relative humidity and sunshine duration decreased significantly at the rate of 0.153 %/year and 6.941 h/year, while annual mean atmospheric pressure rose significantly at the rate of 0.026 hPa/year. And annual mean precipitation exhibited a decreasing trend in the study period, with no statistical significance. Conclusion The annual mean temperature increases significantly during 1951 -2012, with most evident warming in winter. The annual mean relative humidity, sunshine duration decrease gradually. Multi-center researches seem to be essential.