This paper investigates the relationship between financial efficiency and economic growth in Thailand with annual time series during 1991-2015. Financial efficiency measures: (i) bank efficiency in intermediating savings to investment, as measured by the net interest margin (the accounting value of bank's net interest revenue as a share of its average interest-bearing assets) (IMARGIN) and lending-deposit spread (ISPREAD); and (ii) operational efficiency measures, such as overhead costs to total assets; NONILIA while the percentage change of real GDP per capita (real gross domestic product [RGDP]) represents economic growth. The Augmented Dickey-Fuller Test (ADF) of the stationary test shows that all data are stationary at the first difference except ISPREAD is stationary at the second difference. Since all variables are not integrated at the same order, there are no short run and long run relationship between financial efficiency variables and economic growth. The pairwise Granger causality result with 1 lagged length selected by Akaike Information Criterion (AIC), shows that no causality between financial efficiency variables and economic growth and vice versa; and supports the "neutral hypothesis". However, there is a one-way causality linkage between two financial efficiency indicators, lending and deposit interest rate spread, and the ratio of overhead costs to total assets. In other words, the banks' profit from interest spread is used to improve bank efficiency, such as hiring more staff, increase number of branches, and automatic teller machines (ATMs) to improve bank services. Therefore, financial institutions should provide financial services to response customers' needs as the commercialization and modernization of the economy.