A cell observation information processing system includes: a tag acquiring section that acquires, as a search tag for searching for observation information acquired in response to an acquisition order at one time point, tags containing a cell name, first culture tool identifying information for identifying a culture tool for culturing cells under observation, and second culture tool identifying information for identifying a passage-source culture tool; a storing section that stores in an archive section each piece of the observation information acquired at each time point upon assigning thereto the search tag; a search criterion acquiring section that acquires, as a search criterion, tags containing a cell name and first culture tool identifying information; and a retrieving section that searches through the archive section using the acquired search criterion and retrieves search-tagged observation information on cells having undergone passage of culture from a single cell line over a plurality of generations.