A series of uranium(Ⅳ) metaphosphate U(PO

3

)

4

and uranium (Ⅳ) doped thorium metaphosphate crystals Th(PO

3

)

4

:U

4+

were grown from phosphoric acid solution by the method of solution evaporation.Th(PO

3

)

4

and U(PO

3

)

4

crystal compositions were checked and their crystal structures were determined. Th(PO

3

)

4

and ar-U(PO

3

)

4

belong to triclinic system

P

1

or P

1

-space group.β-U(PO

3

)

4

is orthorhombic system

C

mca

-

D

2h

18

space group. The crystallographic data are given. Absorption spectra of U(PO

3

)

4

and the excitation spectra and fluorescence spectra of Th(PO

3

)

4

:U

4+

crystals have been measured at room temperature. Under the excitation with 253nm UV light

U

4+

ions doded in Th(PO

3

)

4

matrix emit a series of wide bands of violet fluorescence

which belong to 6d-5f electronic transition of activated U

4+

ion. When the crystal is excited by 552nm green light

two narrow bands were found at 358nm and 533nm which might belong to

3

P

2

-

3

H

4

and

1

l

6

-

3

H

4

electronic transitions of U

4+

respectively. These types of transition can be explained by up-conversion mechanism. The radiation sheme of U

4+

doped in Th(PO

3

)

4

are given. The fluorescence lifetime of 270nm and 298nm emission of Th(PO

3

)

4

:U

4+

crystals is only about ions. This means that the fluorescent emission is responsible for electric dipole transition