Catechins and alkylresorcinols are important secondary metabolites distributed in food products, sometimes exploited in quality control and/or as markers. The current methods for their quantitative analysis have some disadvantages such as cost, time consuming, and even insensitive or non-selective. Therefore, suitable, efficient methods are still required. As part of our research on new and rapid methods of analyses in plant and food products, a spectrophotometric method to quantify alkylresorcinols and catechins in plant products was developed and fully validated. The colored product by the diazo coupling between olivetol and catechin with diazotized sulfanilic acid was employed to develop the method. The effect of acid and diazonium salt concentration and the reaction time was analyzed. The method was linear in 0.8–8.3 and 0.6–10.2 μg/mL ranges to olivetol and catechin, respectively. Limit of detection and limit of quantification for olivetol and catechin were 0.253/0.768 and 0.106/0.321 μg/mL, respectively. Precision at intra-day and inter-day levels (relative standard deviation (RSD) 1.3–9.7 %) and accuracy (99.0–104.9 %) were also demonstrated. Additionally, the application of the method to plant samples containing alkylresorcinol or catechins was subsequently evaluated, being comparable with conventionally employed methods. Thus, the method demonstrated to be fast, easy, inexpensive, and reliable for quantifying these kinds of metabolites in food products.