A number of animal enclosure windows have been damaged across the site, including the new Southern Cassowary exhibit, with staff forecasting a repair bill of thousands of pounds at a time when the attraction is already struggling financially.
The incident is thought to have happened late on Saturday afternoon when the 40-acre site was busy with bank holiday weekend visitors.
West Midlands Police has been informed of the vandalism.
Zoo director Derek Grove said: “This is simply mindless vandalism which is utterly disheartening following the difficult last 12 months we have endured.
“Like all zoos around the country, we were closed for the majority of the past year and managed to carry on thanks to the generosity of our visitors donating to our online fundraising page and halting our development plans so we could continue caring and feeding for our animals.
“Thankfully we have come out of the pandemic on the other side with some financial losses, but now we are going to have to waste money repairing this damage, which only reduces the funds we have available for the care of the animals.”
This week is Love Your Zoo Week, an initiative aimed at encouraging people to find out more about the work of their local animal attraction during May half term.
Dudley Zoo and Castle finally reopened again in April, as part of step two out of the roadmap out of lockdown.
A West Midlands Police spokesman said: "The damage was reported to us on Saturday, May 29, and we understand the absolute frustration of such a thoughtless criminal act.
"Sadly there are no lines of enquiry for us to pursue, but if anyone has any information, please contact us."
Anyone wishing to donate to the zoo’s Animal Care Fund can do so by visiting www.justgiving.com/campaign/dzcanimalcarefund.
Anyone who visited the site on Saturday and witnesses any suspicious activity is being urged to call West Midlands Police on 101, quoting crime reference number 20/909587/21.