Poly (Lactic Acid) ultrafine fibers were obtained from melt electrospinning in the present work, using a home-made device. To study the effect of main technological parameters on fiber diameter in melt electrospinning, orthogonal design was adopted to examine spinning distance, spinning voltage and melt temperature. Meanwhile, the motion of the jet flow was recorded to help explain the influencing mechanism. Results showed that spinning voltage had the highest impact on the average diameters compared to other considered parameters (spinning distance and melt temperature). fibers with smallest diameter could be produced at 15 kV, 10 cm and 190 o C.