The border between Belize and Mexico is located in the southern part of the state of Quintana Roo, through the city of Chetumal, in Mexico.
To learn more about how to travel between the two countries, please also see Getting from Cancun Mexico to the Cayes in Belize.
The process is the same if you are coming from Belize. There are three ways of travelling between the two countries and as such two ways of going through the border:
The boat leaves the docks in Chetumal around 3:30pm. Once you get to Chetumal you would need to take a taxi to the Belize Express boat docs (about us$5 per taxi). The taxi will drop you off at the entrance to the docs and you would need to buy your ticket (us$50 per person each way) and get processed out of Mexico before you can head towards your boat. The process can take up to 45 minutes depending on how many people are there in line.
When you arrived into Mexico, at the airport they certainly gave you a green form which you had to fill out. Have that handy along with your passport. If you are coming back to Mexico after a few days in Belize, make sure to tell the immigration officer. He may ask you to keep your green form. The exit tax out of Mexico is about us$30. Everyone gets charged the exit fee; even if you paid it with your plane tickets.
Once processed out of Mexico, head out to the docs, find your boat, check-in your luggage, find your seat and relax. The trip takes about two hours.
In Belize, the boat will make its first stop on the island of San Pedro, directly at the immigration docs. You will need to fill up an immigration form and present it with your passport to the officer. There are no fees to get into Belize (exit fee of us$20). Once everyone has been processed into Belize the same boat brings you down to Caye Caulker. You are welcome to stay in San Pedro for the night if you wish.
If you are coming from Belize to Mexico, you will need to catch the first boat off the island to Chetumal around 6:30 to 7:00am depending on which company you buy your tickets from. The boat will make a short stop in San Pedro immigration office to process you out of Belize and charge you the exit fee. Then you get back on the boat for a one and half hour boat ride to Mexico.
Once in Mexico you will get off the boat and fill out a green form to enter Mexico. You will be charged a us$30 entry fee into Mexico. There will be taxis and people changing money at the docs to take you to the ADO bus station (us$5 per taxi).
In Chetumal take a taxi to the market and look for the bus to Belize City. The bus will take you to the Mexican border to check out of Mexico and pay the us$30 fee. You will need to get off the bus with your day pack, passport and the green form you filled out when you first arrived in Mexico (at the airport) to get processed out of the country.
You will then get back on the same bus for a short trip to the Belize side of the border. There you will need to get off the bus again and this time grab your big bags with you across the border. There are no fees to get into Belize (us$20 exit fee). Once you are processed into Belize, find your bus (same bus) and enjoy the ride across this beautiful country. The ride to Belize City is about 4 hours.