An unidentified corrosive liquid was poured onto a Vauxhall Meriva van in Mundon Road, Maldon some time between August 15 and 17.
The liquid was poured on the nearside panels of the white van and caused £500 damage.
A blue Vauxhall Corsa was also damaged overnight on August 16 in Manse Chase, Maldon.
Two door mirrors were kicked off, the aeriel was snapped off and the wiper blades had been pulled off, causing £300 damage.
Anyone with information should call Essex Police on 101.