Physical,chemical and mode-locking properties of pentamethylidyne dye for mode-locking in Nd3+ lasers are given.Several factors which affect the stability of the dye solution with 1,2-dichloroethane as solvent have been found.A method for increasing the stability of the dye solution is presented.Pentamethylidyne dye is proved to be a good and inexpensive dye for mode- locking as comparedwith undecamethylidyne.