Agricultural activity is a feasible alternative in the Amazon as long as technologies are used to generate social, environmental and economic benefits without changing the ecology of the system. In the Amazon region has made ​​work that showed different distribution, geographic presence and incidence of various parasitic genera that affect cattle. The aim of the present study was to evaluate the association between age and nematodes in cattle under free grazing in Canton Arosemena Tola Province Napo - Ecuador. 147 cattle feces were sampled during March 2011 and November 2012. The collection of faeces was carried out during the early hours of the morning and were obtained directly from the rectum of the animal. Coproparasitological analyzes were performed at the Laboratory of Parasitological Diagnosis Vetetinario Chaco-Ecuador. Of the total number of sampled animals were divided into two groups: ≤ twelve months (31) and ≥ to twelve months of age (116). The relationship between nematodes and age was assessed with a test of homogeneity based on Chi-square statistics (P <0.05) and hypothesis test for continuous variables, Student t according to (P <0.05). In Bunostomun, Neoscaris, Trichostrongylus spp, Cooperia, Oesophagostomun, Stronyiloides and Ostertagia parasites are significant (Chi2 (P <0.0001) among children ages twelve months and older than twelve months. There is a very low presence of nematodes in animals older than one year, and 80% expressed no parasites. by contrast 70% of small animals has a high parasite load in the stage of development and growth, certainly impacting on the daily weight gain (ADP). We conclude that there is an association between the presence of nematodes and age of cattle.