  This paper reviews the Chandra deep exposure observations of star forming
regions, rho-Ophiuchi, Orion Molecular Clouds 2 and 3, Sagittarius B2 and
Monoceros R2. The results are; (1) class I protostars are found to exhibit
higher temperature plasma than those of T Tauri stars, (2) heavily absorbed
X-rays are discovered from the candidates of class 0 protostars, (3) hard and
highly variable X-rays are observed from high-mass young stars, and (4) young
brown dwarfs emit X-rays similar to those of low-mass young stars.
