We investigate efficient on-line lossless coding of motion capture (mocap) data in this work. The mocap data consist of a set of curves as the temporal trajectory of variables known as the degrees of freedom (dofs). To achieve compression, we sample each dof's curve temporally, interpolate the curve by a piece-wise Hermite spline as the prediction, and encode residuals with DPCM and Huffman coding. We compare the fixed-interval and the adaptive-interval sampling methods. Both schemes can achieve an averaged bit rate saving of around 80% (or, equivalently, a compression ratio of 20%) with real-time encoding/decoding.