The study focused on structure and fiber length of Java kapok fruit from Pate County, Java Tengah in Indonesia for effective utilization. The internal structure of Java kapok fruit can be divided into two parts: fiber bundle and combination of short staple and seeds. The two parts had little adhesion and large difference in fiber length. Fiber bundle method was put forward to measure fiber length, which had strong correlation with Hand-measured staple length. Furthermore, analysis showed the length of kapok fiber had some correlation with length of fruit, and no correlation with length of middle perimeter. Also, the three parts of fruit: head, middle and tail had no significant difference in fiber length.