We announce the discovery of the transiting hot Jupiter WASP-157b in a 3.95-d orbit around a V = 12.9 G2 main-sequence star .
This moderately inflated planet has a Saturn-like density with a mass of 0.57 \pm 0.10 M _ { Jup } and a radius of 1.06 \pm 0.05 R _ { Jup } .
We do not detect any rotational or phase-curve modulations , nor the secondary eclipse , with conservative semi-amplitude upper limits of 250 and 20 ppm , respectively .