This study aimed to test the effect of online gaming speculative experiences on problem gambling via irrational beliefs in and attitudes toward gambling. Data were obtained from the Korea Center on Gambling Problems, and participants comprised 386 adolescents (female 168, male 218) who currently play online games and have experience with betting games or gambling. The main findings are that (i) online game speculative experience positively influenced gambling attitude (B= 0.172,p< 0.001); (ii) online game speculative experience positively influenced irrational beliefs (B= 0.194,p< 0.001); (iii) online game speculative experience (B= 0.140,p< 0.001), gambling attitude (B= 0.294,p< 0.01), and irrational beliefs (B= 0.689,p< 0.001) was positively correlated with problem gambling. Also, the mediation effect was statistically significant. Policy and practical measures to assess the impact of gaming facilitating speculative experience and for intervening in gambling problems in adolescents are discussed. The results suggest the need to screen, educate, and provide short-term interventions to adolescents with online game speculative experience. Strict assessments, regulation, and surveillance of speculative elements can preserve online gaming as a healthy play culture for the adolescents.