The 2018 Tilia Slovenia Open was a professional tennis tournament played on hard courts. It was the sixth edition of the tournament which was part of the 2018 ATP Challenger Tour. It took place in Portorož, Slovenia between 6 – 11 August 2018.
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
 Ukraine | Sergiy Stakhovsky | 117 | 1 | |
 Austria | Dennis Novak | 136 | 2 | |
 Spain | Adrián Menéndez Maceiras | 143 | 3 | |
 Italy | Gianluigi Quinzi | 162 | 4 | |
| Italy | Salvatore Caruso | 185 | 5 | |
| Italy | Luca Vanni | 191 | 6 | |
| Nino Serdarušić | 193 | 7 | ||
| Italy | Andrea Arnaboldi | 199 | 8 |
The following players received wildcards into the singles main draw:
The following player received entry into the singles main draw as a special exempt:
The following players received entry from the qualifying draw:
The following player received entry as a lucky loser:
Christopher HeymanSee main article: 2018 Tilia Slovenia Open – Singles.
Constant Lestienne def. Andrea Arnaboldi 6–2, 6–1.See main article: 2018 Tilia Slovenia Open – Doubles.
Gerard Granollers / 
Lukáš Rosol def. 
Nikola Ćaćić / Lucas Miedler 7–5, 6–3.
