| POS | Rank | Heat | BIB | ATHLETE | COUNTRY | RESULTS | 
|---|---|---|---|---|---|---|
| 1 | 1 | 4 | JAM | Jamaica U20 | 
 JAM                 | 
                39.54 Q SB | 
| 2 | 1 | 3 | THA | Thailand U20 | 
 THA                 | 
                39.56 Q NU20R | 
| 3 | 1 | 1 | KOR | Korea U20 | 
 KOR                 | 
                39.71 Q NU20R | 
| 4 | 2 | 1 | FRA | France U20 | 
 FRA                 | 
                39.73 q SB | 
| 5 | 2 | 3 | GBR | Great Britain & NI U20 | 
 GBR                 | 
                39.75 q SB | 
| 6 | 2 | 4 | TTO | Trinidad and Tobago U20 | 
 TTO                 | 
                39.77 q SB | 
| 7 | 3 | 1 | AUS | Australia U20 | 
 AUS                 | 
                39.80 q | 
| 8 | 1 | 2 | HKG | Hong Kong, China U20 | 
 HKG                 | 
                39.97 Q | 
| 9 | 3 | 3 | GER | Germany U20 | 
 GER                 | 
                40.06 | 
| 10 | 2 | 2 | SRI | Sri Lanka U20 | 
 SRI                 | 
                40.14 | 
| 11 | 3 | 2 | CHN | PR of China U20 | 
 CHN                 | 
                40.18 | 
| 12 | 4 | 1 | ESP | Spain U20 | 
 ESP                 | 
                40.21 | 
| 13 | 3 | 4 | NGR | Nigeria U20 | 
 NGR                 | 
                40.28 SB | 
| 14 | 4 | 4 | DEN | Denmark U20 | 
 DEN                 | 
                40.31 SB | 
| 15 | 5 | 4 | MEX | Mexico U20 | 
 MEX                 | 
                40.34 NU20R | 
| 16 | 4 | 2 | ZIM | Zimbabwe U20 | 
 ZIM                 | 
                40.40 NU20R | 
| 17 | 4 | 3 | CZE | Czechia U20 | 
 CZE                 | 
                40.41 | 
| 18 | 6 | 4 | ITA | Italy U20 | 
 ITA                 | 
                40.44 SB | 
| 19 | 5 | 2 | FIN | Finland U20 | 
 FIN                 | 
                40.46 SB | 
| 20 | 5 | 1 | GRN | Grenada U20 | 
 GRN                 | 
                40.63 NU20R | 
| 21 | 5 | 3 | CAN | Canada U20 | 
 CAN                 | 
                40.70 SB | 
| 22 | 7 | 4 | POL | Poland U20 | 
 POL                 | 
                40.99 | 
| 23 | 6 | 3 | CHI | Chile U20 | 
 CHI                 | 
                41.62 | 
| 24 | 6 | 2 | PER | Peru U20 | 
 PER                 | 
                41.80 SB | 
| 25 | 7 | 3 | BUL | Bulgaria U20 | 
 BUL                 | 
                41.92 SB | 
| 2 | BRA | Brazil U20 | 
 BRA                 | 
                DNF | ||
| 2 | USA | United States U20 | 
 USA                 | 
                DNF | ||
| 1 | SUI | Switzerland U20 | 
 SUI                 | 
                DNF | ||
| 1 | RSA | South Africa U20 | 
 RSA                 | 
                DQ | ||
| 3 | JPN | Japan U20 | 
 JPN                 | 
                DQ | ||
| 4 | ECU | Ecuador U20 | 
 ECU                 | 
                DNS |