In this paper, the notion of injectivity with respect to order dense embeddings in the category ofS-posets, posets with a monotone action of a pomonoidS on them, is studied. We give a criterion, like the Baer condition for injectivity of modules, or Skornjakov criterion for injectivity ofS-sets, for the order dense injectivity. Also, we consider such injectivity forS itself, and its order dense ideals. Further, we define and study some kinds of weak injectivity with respect to order dense embeddings, consider their relations with order dense injectivity. Also investigate if these kinds of injectivity are preserved or reflected by products, coproducts, and direct sums ofS-posets.