The influences of the flux KCl or KF on the XRD patterns, cell parameters, crystal morphology, and spectral properties of the phosphor LaMgB_5O_(10)∶Ce~(3+), Mn~(2+) are studied. The results indicate that as 4.2%, 8.6%, 12.8% KCl and 5.3%, 10.5% KF are added individually into the phosphor (La_(0.85)Ce_(0.15)) (Mg_(0.9)Mn_(0.1)) B_5O_(10), some peaks of the XRD patterns are intensified and cell volumes are decreased. A small amount of Cu mono-crystal typed phase appears as more than 5% KCl is added. There are six hexagonal crystal-faces and eight triangular crystal-faces attributed to the {100} and {111} respectively. When 15% KCl is added into the phosphor, multi-faced regular crystals are formed and the crystal self-regulation appears. The emission intensity of 5d→4f ((()~2F_(5/2),) (()~2F_(7/2))) of Ce~(3+) and (()~4G→()~6S) of Mn~(2+) increases up 3.41 and 2.36 times respectively. The influences of the flux KCl or KF on the XRD patterns, cell parameters, crystal morphology, and spectral properties of the phosphor LaMgB_5O_ (10): Ce ~ (3+), Mn ~ (2+) are studied. (Mg_ (0.9) Mn_ (0.1)) B_5O_ (10), some peaks as 4.2%, 8.6%, 12.8% KCl and 5.3%, 10.5% KF were added individually into the phosphor of the XRD patterns are intensified and cell volumes are decreased. A small amount of Cu mono-crystal typed phase appears as more than 5% of KCl is added. There are six hexagonal crystal-faces and eight triangular crystal-faces attributed to the {100 When 15% KCl is added into the phosphor, multi-faced regular crystals are formed and the crystal self-regulation appears. The emission intensity of 5d → 4f ((() ~ 2F - (5/2) () ~ 2F_ (7/2))) of Ce ~ (3+) and (() ~ 4G → () ~ 6S) of Mn ~ (2+) increase up 3.41 and 2.36 times respectively.