Papyrus Oxyrhynchus 135 (P. Oxy. 135 or P. Oxy. I 135) is the third in a series of Oxyrhynchus papyri (133–139) concerning the family affairs of Flavius Apion, his heirs, or his son. This one is a deed of surety, written in Greek and discovered in Oxyrhynchus. The manuscript was written on papyrus in the form of a sheet. The document was written on 21 March 579. Currently it is housed in the Egyptian Museum (10018) in Cairo.