PURPOSE: To readily produce a nonwoven fabric of ultrafine fiber optimum as a filter, wiper, etc., using an ordinary card machine and a water jet machine.

CONSTITUTION: A conjugate synthetic fiber capable of splitting is carded to form a web containing split fiber and then the conjugate synthetic fiber is further split with a water jet, and simultaneously, fibers of the above-mentioned web is mutually interlaced and part of the split nonwoven fabric is thermally fused. Thereby, a split nonwoven fabric having good process-passing property and containing uniform ultrafine fiber is readily obtained, and the resultant split nonwoven fabric contains 10-80wt.% fiber having ≤0.5 denier fineness and has excellent physical properties such as feeling by hand and air diffusibility in addition to excellent cloth strength, and is suitable for filter, wiper, base for artificial leather, etc.