This aim of this research is to analyse the effect of planting season factor on the purchasing intensity of liquid leaf fertilizer products by onion farmers in Brebes, Central Java Indonesia. This research was conducted by using a survey approach through interviews of 100 respondents of onion farmers on April until May 2017. The effect of planting season factor on the purchasing of liquid leaf fertilizer on the purchasing intensity were analysed by using t-independent sample test and dummy regression analysis. The result shows that intensity of the use of liquid fertilizer was affected by the planting season. The purchasing intensity of liquid fertilizer products by the farmers in wet season (10.26 litter ha-1) was higher than the dry season (4,81 litter ha−1)