Grice's conversational maxims have been one of the most influential pragmatic theories up to now. The primary purpose of this study was to measure the comprehension of Iranian intermediate EFL learners in terms of English humor based on Grice's non-observed conversational maxims. Moreover, this study intended to find which of Grice's non-observed conversational maxims make it difficult for EFL learners to comprehend the discourse of English humor. Using a mixed-methods design, 300 participants were selected from different age groups. The selected participants were 129 females and 171 males whose ages varied from 19 to 37. In the final phase of the study, four students were selected based upon their willingness and availability to take part in a qualitative phase. Results showed that among the four Grice's non-observed conversational maxims, the quantity maxim (0.75) had had the highest mean score, resulting as the easiest maxim and the quality maxim (0.41), which had the lowest mean score, was the most challenging maxim. The results of the qualitative data confirmed the quantitative results. Quantity was found to be the easiest maxim in the English Humor Comprehension Test (EHCT), and Quality was the most challenging maxim.