Abstract. We present the optical variability studies of X-ray sources in NGC 1399 with the HST ACS observations. NGC 1399 is a giant elliptical galaxy in the center of Fornax cluster, 36 X-ray point sources have been identified by Chandra. We searched for the optical counterparts to these sources in HST archival images. Out of 36, twenty six of them falling in the HST field of view and 22 of them having potential counterparts within an error circle of few arcsec. Two of them show significant variability of ∼0.4 magnitude between two F475W observations separated by 23 months, while the others have a variation less than 0.1. The X-ray luminosity of these optically varying sources is less compared to ultra-luminous X-ray sources (less than 10³⁹ erg s^-1). The optical variability indicates they may be background AGNs.