An optic fiber adaptor includes two flexible engaging members and two positioning walls cooperating with one another to define an insertion slot. Each engaging member has a first inclined surface and a second inclined surface disposed behind the first inclined surface. A distance between the first inclined surfaces of the engaging members decreases rearwardly so as to facilitate pushing of a casing body of a ferrule assembly into the insertion slot. A distance between the second inclined surfaces of the engaging members decreases forwardly so as to facilitate pulling of the casing body out of the insertion slot. An optic fiber connecting device having the optic fiber adaptor is also disclosed.