Thirty five species of oyster pelecypods are described from the Middleand Upper Jurassic of Poland, belonging to 7 genera and 3 subfamilies: Ostreinae, Vialov 1936, Gryphaeinae, Vialov, 1936 and Exogyrinae, Vialov, 1936. Morphology of species, their development and individual variability are investigated. The lithological and geological relationships of the area under investigation, the influence of environment onto the shell morphology, examples of functional and structural adaptations of Ostreidae and shell microstructure are characterized. The remarks on the phylogeny of Ostreidae are completed by an introduction of two development stages: Catinula and Nanogyra. The systematic position of Nanogyra nana Beurlen, 1958 is discussed.