Soil calcium (Ca) determines several characteristics of soil fertility and affects many plant functions after absorption. It is necessary to develop a method to quickly determine soil Ca content in situ because soil Ca content can vary considerably in natural environments. Laboratory determination of Ca is laborious and costly. This study assessed the potential of field portable X-ray fluorescence (FPXRF) to be used in soil Ca determination. The consistency, repeatability, and accuracy of FPXRF are carefully examined using both artificial and natural soil samples. The effects of sample treatments including drying, bagging, grinding, and sieving on FPXRF are also investigated. Results show that FPXRF can detect and quantify total soil Ca content rapidly, accurately, and consistently with standard or specific calibration.