Getting to Werribee Open Range Zoo by Public Transport is easy. 

Step 1
Catch a train from the Melbourne CBD to Werribee (Werribee Line)
or 
Catch a train from Geelong to Werribee.

Step 2
Catch a bus from Werribee station to the Zoo. Buses depart at the following times:

Monday to Friday
Station to Zoo:      8.58am    10.18am     11.38am    12.58pm     4.58pm
Zoo to Station:      9.13am    10.33am     1.53pm      2.58pm      5.13pm  

Saturday
Station to Zoo:      8.58am     10.18am     11.38am     12.58pm     2.18pm     4:58pm
Zoo to Station:      9.13am     10.33am     11.53am     2:58pm      4.21pm        

Please note:
Above times are subject to change, and service is not provided on Sundays or Public Holidays at this time.

Please check http://www.viclink.com.au/ for latest news and train times.