The Solomon Islands is currently experiencing a change in disease burdens, from communicable to non-communicable diseases. Obesity is one of the leading non-communicable diseases causing death. Urgent action is needed to decrease the high economic and personal costs associated with obesity. This study proposes to determine behavioral and socioeconomic factors associated with obesity among different sex and age groups in an urban area of the Solomon Islands. In 2016, a cross-sectional study was conducted among adults aged 20 to 80 in Honiara, the capital of the Solomon Islands. Anthropometric measurements and a survey of socioeconomic status (SES) and behavioral status were conducted among 176 participants using a questionnaire. Multiple linear regression analysis was used to identify the socioeconomic factors significantly associated with higher body mass index (BMI) by age group. The study found a high prevalence of overweight (34%) and obesity (48%) in both sexes. Multiple linear regression analysis found that having a high-income level and being married were positively associated with higher BMI among young adults. In the middle age groups, the highest income level was positively associated with higher BMI. Young and middle-aged adults with a high SES might consume higher calorie food, contributing to weight gain, but this needs confirmation. Moreover, getting married might lead to more consistent meals and weight gain among the young age group. These findings suggest that health professionals have to consider the influence of income level and marital status on lifestyle choices when planning interventions that promote healthy lifestyles.