Short-crested wave in real sea condition is defined as the linear summation of a series of long-crested waves propagated to different directions, where the magnitude and directions are randomly generated. Also, it is complex and three dimensional. In this paper, an experimental and numerical study on the truss spar responses subjected to long and short-crested waves are presented. The experimental study on a typical truss spar model subjected to long and short-crested waves were performed in the wave tank of Offshore Laboratory in Universiti Teknologi PETRONAS. In the study, physical motions in surge, heave and pitch of the model with four linear spring mooring lines restrained were measured. Also, a numerical MATLAB code incorporating the short-crestedness of the waves to predict the dynamic analysis of the truss spar was developed. The results were obtained in terms of Response Amplitude Operator (RAO) for surge, heave and pitch motions using both methods. The predicted RAO were compared with the measured RAO and they agreed fairly well. Also, it was observed that the responses for short-crested waves were much lower compared to the responses for long-crested waves. Copyright © 2013 by the International Society of Offshore and Polar Engineers (ISOPE).