We demonstrated for the first time an autocorrelator based on two-photon absorption of ZnSSe photodetectors which is capable of measuring femtosecond laser pulses from 800 to 400 nm. This antocorrelator has a very broad bandwidth, high sensitivity and is capable of measuring laser pulses with high repetition rate. These results could lead to cost effective ultrafast autocorrelators with a single detector head to cover the whole of visible to near UV spectral region. Using a ZnMgS photodetector with a larger bandgap enables the autocorrelator to be more sensitive at 400 nm and extends the responsivity further into the ultraviolet wavelength of 350 nm.