The prevalence of obesity and weight gain is higher in the working class, but we know little about class differences in practices used to control weight. This study examined associations between self-reported measures of social class (upper, middle, or working class), weight control practices, and weight among a cohort of 11,589 mid-aged women (aged 47–52) participating in the Australian Longitudinal Study on Women's Health (ALSWH). A multivariate model tested whether mean weight change over a two-year period differed by social class after adjusting for area of residence, age, education, baseline BMI, and smoking. Working-class women gained significantly more weight at 1.27 (0.07) kg (95% CI: 1.12–1.42) over 2 years, compared with middle/upper-class women at 1.01 (0.07) kg (95% CI: 0.88–1.15). They were significantly more likely to use potentially harmful weight control practices than middle/upper-class women (8.9%) (Chi-squared test = 30.65, p < 0.0001), and less likely to meet physical activity recommendations. The study provides longitudinal evidence from a nationally representative sample of women that social class is related to weight gain, and to certain weight control practices. The findings have implications for the development of weight gain prevention programs for socially disadvantaged groups.