Moving particle semi-implicit (MPS) method is widely used for the free surface flow analysis. In small scale problems, the surface tension is dominant. There are two approaches to calculate surface tension in particle methods. One is based on continuum mechanics governing equation which needs the normal vector and the curvature calculation. However, it requires complex formulation. The other is introducing inter-particle potential force. It is known that surface tension can be deduced from inter-molecular force. We propose inter-particle force whose potential is similar to the molecular potential. We reveal the inter-relation between this potential force and the surface tension coefficient used in continuum mechanics. The surface tension can be calculated using this inter-particle potential force. The oscillation cycle roughly agrees with the theoretical value. It is also important to introduce the contact angle to the solid wall, as well as the surface tension. The inter-particle force is also available to model the contact angle. The potential force ratio between fluid-fluid and fluid-wall can be derived from Young’s equation. Using this theoretical ratio of potential force, a larger contact angle appears, if we give a smaller potential force ratio.Copyright © 2007 by ASME