purpose of the present paper is to make a linguistic analysis of the Judeo-Arabic manuscript Or. 7768 preserved in the British Library, which belongs to the so-called Cairo Geniza collection. This manuscript contains two versions of purim mitzrayim (Purim of Egypt or Cairo) written in Hebrew and Arabic, the latter, of course, using the Hebrew characters.According to the parameter of the phonetic correspondence between Hebrew letters and Arabic sounds which each letter stands for, Judeo-Arabic documents can be roughly classified into four periods; i) Early Judeo-Arabic (8C.-10C.), which is written in Early Vulgar Judeo-Arabic Spelling; ii) Classical Judeo-Arabic (10C.-15C.), which is written in Classical Judeo-Arabic Spelling; iii) Later Judeo-Arabic (15C.-18C.), which is written in Later Judeo-Arabic Spelling; and iv) Modern Judeo-Arabic (19C.-). The language of the manuscript in question basically belongs to the third variety of Judeo-Arabic, but shows many linguistic features characteristic of Classical Judeo-Arabic (Spelling).