The growth behavior of Cr ad-layer on W(110) surface was studied with scanning tunneling microscopy. Two-dimensional islands are formed at Cr coverage of similar to0.3 monolayer, suggesting typical homogeneous nucleation. The growth mode undergoes a-transition to the formation of organized nano-scale lines at the coverage of >0.5 monolayer. The grown lines are aligned along [(1) over bar 11] and [1 (1) over bar1] directions at room temperature. At an elevated temperature, trenches are formed in a two-dimensional wetting layer with high aspect ratios. Possible microscopic origins for the observed structures are discussed. (C) 2003 Elsevier B.V. All rights reserved.