A promising route for the quantitative transesterification of soybean oil (SBO) with methanol to biodiesel (FAMES) at room temperature is described using the Merrifield resin-supported catalyst resin-N3P(MeNCH2CH2)(3)N. This catalyst was recycled 11 times, although its activity decreased with time. Factors possibly responsible for catalyst deactivation are presented. Interestingly, the polymer-supported catalyst was twice as active as the homogeneous analogue PhCH2N3P(MeNCH2CH2)(3)N in this reaction. The SBO/methanol ratio in our protocol was 1:33, and the biodiesel obtained from our protocol met the American Society for Testing and Materials (ASTM) D-874 standard for sulfated ash.