Hand gesture is one of the most expressive, natural and common types of body language for conveying attitudes and emotions in human interactions. In this paper, we study the role of hand gesture in expressing attitudes of friendliness or conflict towards the interlocutors during interactions. We first employ an unsupervised clustering method using a parallel HMM structure to extract recurring patterns of hand gesture (hand gesture phrases or primitives). We further investigate the validity of the derived hand gesture phrases by examining the correlation of dyad's hand gesture for different interaction types defined by the attitudes of interlocutors. Finally, we model the interaction attitudes with SVM using the dynamics of the derived hand gesture phrases over an interaction. The classification results are promising, suggesting the expressiveness of the derived hand gesture phrases for conveying attitudes and emotions.