This study entails an analysis of the technical efficiency of natural rubber production by state farms in Vietnam. A time-varying stochastic frontier production function model for unbalanced data is estimated for 33 farms. Individual farm technical efficiencies are reported and discussed. One of the main results concerns the bimodal distribution of technical efficiency indices. A few farms operate near the production frontier while the bulk operate well away from the frontier. Some implications are drawn from the results as a guide to future policy research work in the rubber industry in light of recent moves by the Vietnamese government towards economic reform.