We report on the spectral analysis of RXTE and INTEGRAL data of the 2005 April outburst of the transient Atoll source Aql X-1 .
Although this outburst is one of the faintest ever detected for this source in the soft X-rays ( RXTE /ASM ) , one of our INTEGRAL observations , taken close to the soft X-ray peak , shows that the source flux was quite high , with a 20-200 keV flux of 2.05 \times 10 ^ { -9 } erg cm ^ { -2 } s ^ { -1 } .
On this occasion we detect the source up to 150 keV for the first time .
We compare and discuss the similarity of the source behavior with that of black hole transients especially XTE J1550 - 564 .