Subsititute Klara Cvrckova scored the only goal of the game in the second-half to seal the victory for the hosts with the second game between the two sides tomorrow.
Ireland had a number of chances as just before half-time, Shelbourne LFC striker Alannah McEvoy combined well with Andrea Trill down the right but put her effort narrowly wide of the post.
Czech Republic took the lead nine minutes into the second-half after Ireland failed to clear the ball properly and Cvrckova found the net from 25 yards to score the only goal of the game to give the Czechs the win.
Ireland continued to create chances in the second-half but couldn't find the equaliser and Republic of Ireland WU17 & WNT Head Coach Colin Bell was disappointed with the result.
Bell said: "The first-half was ok, we were well organised and had a number of good moments. We didn't allow them any space and definitely should have scored but you could tell that the team needed more time to gel.
"The second-half, we got scrappy and we made a bad mistake which lead to the goal. We could have avoided that so that was disappointing. There are plenty of positives though as there are plenty of new additions to the group and we had some great spells and attacked well.
"It was a typical first game together for the girls really as we took too long in possession at times so we need to get used to moving the ball quicker. I'm sure that will come as we've got another game on Friday so I'm sure we'll see that improve.
"It's a big step the team has to make up to this level but the potential is there for sure. We made four substitutions today so I won't be making wholesale changes for Saturday's match. We'll make changes but it won't be like ten changes as we want to try and give the team some stability.
"We need to keep the core of the team together as match practice is key but that's the good thing about having two matches as we can give most players a decent run."
The WU17s have another game against Czech Republic on Saturday which will be their final game before their 2018 European Championships qualifying campaign starts against Romania, Greece and Bosnia-Herzegovina.
Republic of Ireland WU17 side: Kelly (GK), Lobato (Foley 41), O'Mahony, McGovern, Fahey, Mackey (C), Whelan (Trill 41), Ziu (Masterson 70), McEvoy, Fowler (Boyle Carr 63), Atkinson.
Republic of Ireland WU17 Squad
Goalkeepers: Rachel Kelly (Shelbourne LFC), Courtney Maguire (Cabinteely).
Defenders: Eabha O'Mahony (Lakewood), Roisin McGovern (UCD Waves), Leah Brady (Lucan United), Niamh Murphy Halstead (Home Farm), Rachel O'Regan (Carrigaline)
Midfielders: Doireann Fahey (Peamount United), Isibeal Atkinson (Shelbourne LFC), Megan Mackey (Chelsea), Jessica Ziu (Shelbourne LFC), Lucia Lobato (Galway WFC), Aoife Slattery (Ferrybank), Ciara Fowler (Home Farm).
Attackers: Alannah McEvoy (Shelbourne LFC), Zara Foley (Lakewood), Amy Doyle Carr (Sion Swifts), Louise Masterson (Peamount United), Emily Whelan (Shelbourne), Andrea Trill (Cregmore Galway).