Abstract: Theranostics, combining therapy and diagnosis, is an appealing approach for chemotherapy in medicine which exhibits improved biodistribution, selective cancer targeting ability, reduced toxicity, masked drug efficacy, and minimum side effects. The role of diagnosis tools in theranostics is to collect the information of the disease state before and after specific treatment. Currently, small conjugate-based systems have received much attention for cancer treatment and diagnosis. Relative to the normal tissues, tumor microenvironment shows great difference, including acidic excessive expression of various enzymes as well as low oxygen. In this review, the latest developments on small conjugate based theranostic agents for tumor treatment and diagnosis using fluorescence were summarized.