By Public Transportation:
It will take 15-30 minutes from Chiang Mai downtown to Chiang Mai Zoo.
"Rod-Dang" or Red Taxi
In lieu of a local bus service, locals get around the city on songthaew (สองแถว). These covered pick-up trucks have two long bench seats in the back (songthaew means "two rows" in Thai), and travel fixed routes picking up passengers en route who are going the same way. Some can also be hired outright.
The colour of the songthaew indicates its general route or usage. Most common by far are red songthaews (called rod daeng, red truck), which don't follow a specific route and roam the main streets around markets, temples, or the bus/train stations. These are the most convenient to take if you are going somewhere specific. Prices must be negotiated. but expect 20 baht anywhere within the city walls and 40-60 baht outside. Because of the city's somewhat irrational road design, especially inside the old walls, the driver may be forced to take a circuitous route to get to a nearby destination, but it will make no difference in the fare.
Fixed route songthaews congregate around Warorot Market. From Warorot Market, white songthaews travel to the eastern suburban city of Sankampaeng, yellowsongthaews travel to Mae Rim in the north, blue songthaews travel to Sarapee and Lamphun in the south, and green songthaews travel to Mae Jo in the northeast. They all charge a 20 baht flat rate.
From Pratu Chiang Mai Market, songthaews also travel to Hang Dong (20 baht) and San Patong, southwest of Chiang Mai.
To catch a songthaew; approach a waiting driver or flag one down on the street, state your destination and if the driver is going that direction he will nod in agreement and give you a price. Negotiate a lower fare if you wish. The price agreed to should be per person; it's a good idea to confirm this with the driver before you leave. On reaching your destination, ring the buzzer on the roof to tell the driver to stop, or most likely the driver will pull over, wait for you to get out and pay.