Charity One25 said the service would be offered after they had closed the night-time drop-in centre which has run as a three-month pilot since April.
Gill Nowland, from One25, said they were "working flexibly" to help women at "the time they need it the most".
One25 hopes to pilot late night Friday outreach in August and September.
Ms Nowland said they had "gained a great deal of learning" from the three-month night-time drop-in centre pilot, which started in April and is based in Grosvenor Road in St Pauls.
She said: "Our night drop-in pilot has helped women at their most desperate: fleeing violence with no-one to turn to and nowhere safe to go.
"However, we have now learned that Friday is one of the women's busiest working nights. To meet them where they are, we will close our night drop-in doors at the end of July and start providing Friday night outreach until 3:30am."
A service user, who preferred not to give her name, said: "The van going out until 3am on a Friday night is a much better option than night drop-in because the service will be made much more use of.
"Service users will be able to speak more face-to-face with the workers as they are more likely to be working. Sex workers will be able to report incidents better regarding attacks or any funny behaviour.
"Service users will be able to gain access to food more easily and condoms as they are more likely to be in the area where the van is."
A late Friday night service for street sex workers in Bristol is opening to provide extra support on "one of the women's busiest working nights".