Despite the awareness of the importance of mental health problems among adolescents in developed countries like Australia, inequality has not been widely researched. This study, is therefore, aimed to measure and compare household income-related and area-based socioeconomic inequalities in mental health problems (bullying victimization, mental disorders-single and multiple, self-harm and suicidality-ideation, plan and attempt) among Australian adolescents aged 12-17 years. Young Minds Matter (YMM)-the 2nd national cross-sectional mental health and well-being survey involving Australian children and adolescents conducted in 2013-14, was used in this study to select data for adolescents aged 12-17 years (n = 2521). Outcome variables included: bullying, mental disorders, self-harm, and suicidal ideation, plan and attempt. The Erreygers's corrected concentration index (CI) approach was used to measure the socioeconomic inequalities in mental health problems using two separate rank variables-equivalised household income quintiles and area-based Index of Relative Socioeconomic Advantage and Disadvantage (IRSAD) quintiles. The prevalence of mental health problems in the previous 12-months among these study participants were: bullying victimization (31.1%, 95% CI: 29%-33%), mental disorder (22.9%, 95% CI: 21%-24%), self-harm (9.1%, 95% CI: 8%-10%), suicidal ideation (8.5%, 95% CI: 7%-10%), suicidal plan (5.9%, 95% CI: 5%-7%) and suicidal attempt (2.8%, 95% CI: 2%-3%). The concentration indices (CIs) were statistically significant for bullying victimization (CI = -0.049, p = 0.020), multiple mental disorders (CI = -0.088, p = <0.001), suicidal ideation (CI = -0.023, p = 0.047) and suicidal attempt (CI = -0.021, p = 0.002), implying pro-poor socioeconomic inequalities based on equivalized household income quintiles. Similar findings revealed when adolescents mental health inequalities calculated on the basis of area based IRSAD (Index of Relative Socio-economic Advantage and Disadvantage) quintiles. Overall, adolescents from economically worse-off families experienced more mental health-related problems compared to those from economically better-off families. This has implications for prevention strategies and government policy in order to promote mental health and provide equitable healthcare facility.