This paper examines the influences of accessibility to R&D on the export diversity in Swedish regions. A theoretical model with fixed R&D cost predicts that spatial knowledge spillovers generate external economies of scale in R&D activities. These external effects are presumed to increase regions' innovative capacity. Moreover, the model implies that the effects of R&D on regional export performance are reflected by the size of the export base rather than by the export volumes. The empirical analysis focuses on three different indicators of export diversity: the number of exported goods, the number of exporting firms and the number of export destinations. The hypothesis that regional accessibility to R&D facilities in the private business sector, on the one hand, and university research departments on the other hand, increases the export diversity in regions is tested in a spatial cross-regressive model. Since knowledge cannot be regarded as a spatially trapped resource the empirical analysis includes two measures of R&D accessibility: intra-regional and inter-regional. The empirical results indicate that the three indicators of regional export diversity are positively affected by the intra-regional accessibility to company R&D in commodity groups that have a relatively high R&D-intensity in production. Inter-regional accessibility to company R&D has significant positive impacts on the number of export goods and the number of export destinations also in less R&D-intensive industries. In the case of university R&D, the empirical results are weaker, in particular in the case of intra-regional accessibility. Yet, the inter-regional accessibility to university R&D has a significant positive impact on the number of export goods and the number of export destinations in the majority of commodity groups.