Paramagnetic resonance of

{Yb}^{3 +}

has been observed in single crystals of CaW

O_{4}

at 20°K and 3 cm. A tetragonal as well as two rhombic spectra were found. The tetragonal spectrum is fitted to an axial spin Hamiltonian with

g_{II} = 1.058 \pm 0.002

g_{⊥} = 3.920 \pm 0.005

| {}^{173}A | = (77 \pm 1) 10^{- 4}

{cm}^{- 1}

| {}^{173}B | = (285 \pm 1) 10^{- 4}

{cm}^{- 1}

| {}^{173}P | < {2.10}^{- 3}

{cm}^{- 1}

| {}^{171}A | = (279 \pm 3) 10^{- 4}

{cm}^{- 1}

| {}^{171}B | = (1034 \pm 3) 10^{- 4}

{cm}^{- 1}

. The rhombic spectra have the

y

and

z

axes in the {110} planes. One has the

z

axis at 6°±1° to the crystallographic

c

axis and

g_{x} = 3.012 \pm 0.005

g_{y} = 4.788 \pm 0.005

g_{z} = 0.975 \pm 0.003

. The other has the

z

axis at 7°±1° to the

c

axis and

g_{x} = 4.155 \pm 0.005

g_{y} = 3.704 \pm 0.005

g_{z} = 1.155 \pm 0.003

. The spectra arise from

{Yb}^{3 +}

ions at

{Ca}^{2 +}

sites and the rhombic symmetry is caused by charge compensation at next-nearest-neighbor

{Ca}^{2 +}

sites. The possibility of

W^{6 +}

substitution is discussed.

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