This study deals with the performance evaluation of writing for designing handwriting instruments ergonomically. Experimental tests were executed on ballpoint pen., felt-tip pen, pencil, sharp-pencil, and fountain pen for ease of use and reduction of the muscles fatigue. The writing time and the degree of comfort of writing by subjects were measured on the diameters of five writing instruments. The results indicated that the ballpoint pen was rated significantly superior to the others in writing speed attribute and the instrument with the least fatigue was the fountain pen. There was a significant interaction effect between the types of instruments and their size in diameters. The diameter of instruments for considering time and comfort together was verified that the size of 9.5mm was efficient for ballpoint pen, the size of 8.1mm for felt-tip pen, the size of 7.5mm for pencil, the size of 8.2mm for sharp-pencil, and the size of 9.1mm for fountain pen.