The objectives of this study are to examine the trends, assess socio-economic differentials, and to determine whether declines in desired family size are associated with declines in fertility in Kenya. Using the synthetic cohort analytical method, the study found a consistent and monotonic decline in desired family size over the periods studied. These declines are highly correlated with declines in total fertility rate (TFR) over the same period, thereby suggesting that observed declines in TFR are probably driven by changes in desired family size. The analysis of the differentials reveal that women's education, women's work and income status, ownership of durable goods, husband's desired family size, knowledge of modern contraception and ethnicity account for significant variations in desired family size.