Enhancing intelligence through working memory training is an attractive concept, particularly for middle-aged adults. However, investigations of working memory training benefits are limited to younger or older adults, and results are inconsistent. This study investigates working memory training in middle age-range adults. Fifty healthy adults, aged 30-60, completed measures of working memory, processing speed, and fluid intelligence before and after a 5-week web-based working memory (experimental) or processing speed (active control) training program. Baseline intelligence and personality were measured as potential individual characteristics associated with change. Improved performance on working memory and processing speed tasks were experienced by both groups; however, only the working memory training group improved in fluid intelligence. Agreeableness emerged as a personality factor associated with working memory training related change. Albeit limited by power, findings suggest that dual n-back working memory training not only enhances working memory but also fluid intelligence in middle-aged healthy adults.