A 3-dimensional fiber probe based on orthogonal micro focal-length collimation (MFL-collimation) is proposed for the measurement of micro parts with high aspect ratios. The probe consists of a fiber stylus which acts as a micro focal-length cylindrical lens (MFLC-lens) of the two orthogonal MFL-collimation optical paths and a probe tip fixed on the free end of the fiber stylus for touching the workpiece. The fiber stylus will deflect (deflection mode) or buckle (buckling mode) under contacts, and the deflection or buckling of the fiber stylus will cause corresponding shifts of the fringe images of the two orthogonal MFL-collimation optical paths. Therefore, the 3-dimensional displacements of the probe tip are transformed into the centroid position shifts of the zero-order fringe images. Experimental results indicate that the fiber probe has a measuring capability in 3-dimensional tactility, and a radial and axial resolution of 5 nm and 3 nm can be obtained respectively. The probe is easily applied in the measurement of micro parts because of its high resolution, low cost, high measurable aspect ratio, low probing forces and capability in three-dimensional tactility.