Abstract : Mathematical Morphology (MM) offers a generic theoretical framework for data processing and analysis. Nevertheless, it remains es- sentially used in the context of image analysis and processing, and the attempts to use MM on other kinds of data are still quite rare. We believe MM can provide relevant solutions for data analysis and processing in a far broader range of application fields. To illustrate, we focus here on textual data and we show how morphological operators (here the mor- phological segmentation using watershed transform) may be applied on these data. We thus provide an original MM-based solution to the the- matic segmentation problem, which is a typical problem in the fields of natural language processing and information retrieval (IR). More precisely, we consider here TV broadcasts through their transcrip- tion obtained by automatic speech recognition. To perform topic seg- mentation, we compute the similarity between successive segments using a technique called vectorization which has recently introduced in the IR field. We then apply a gradient operator to build a topographic surface to be segmented using the watershed transform. This new topic segmenta- tion technique is evaluated on two corpora of TV broadcasts on which it outperforms other existing approaches. Despite using very common mor- phological operators (i.e., the standard Watershed Transform), we thus show the potential interest of MM to be applied on non-image data.