The visitors kicked off their season with a 13-12 home success against the Blues, but will find this an altogether tougher assignment, in west Wales.
The other game sees the Ospreys travel to Glamorgan Wanderers to face the Blues.
Scott Andrews, who scored one of the Blues' consolation tries last week, starts as captain, whilst in the Dragons' side, senior full back Jason Tovey is included.
His eight point haul at Ebbw Vale last week was crucial in the end as it earned the Dragons only a second win, at any level, in this season's competition.
Aaron Coundley, who has spent time on the bench for the Dragons' senior side this season, is named in the 22 as is the highly rated Ieuan Coombs.
Under 20's Blues v Ospreys 7.15pm kick off at Glamorgan Wanderers
Cardiff Blues: J Loxton; L Fear, H Allen, D Gunter, R Healey; J Murphy, G Lucas; T Price, R Williams, S Andrews (capt), N Huntley, D Partridge, K Dacey, J Thomas, B Morgan. Replacements: M Howells, B Lee, J Navidi, S Studley, T Rowlands, R Locke, J Deacon
Scarlets: D Newton; J Davies, S Soul, S Williams, N Davies; D Etteridge, T James (capt); O Evans, L Lewis, S Gardner, J Davey, S Jones, E Lloyd, J Davies, R Decapenter. Replacements: A Howells, G Flynn, L Kendall, H Boot, G Davies, N Reynolds, M Evans
Dragons: J Tovey; O Halford, A Hughes, M Pewtner, N Preece; D Langdon, D Jones; D Watchurst, C Fillier, S Maguire, S Pailor, A Sweet (capt), M Allen, R Jenkins, J Thomas. Replacements: A Coundley, R Price, L Bray, T Falatau, C Davies, I Coombs, T Driver