To ensure ignition and stable combustion of ammonia in engines, increasing the pressure inside the combustion chamber can be an effective strategy, although this can lead to the knock phenomenon. To predict this occurrence through simulations, accurate kinetic mechanisms for ammonia oxidation are required to reliably predict auto-ignition. Therefore, a robust experimental database of Ignition Delay Times (IDTs) is essential. In this study, IDTs for pure ammonia fuel were measured using a rapid compression machine under high-pressure conditions (40–70 bars) and low to intermediate temperatures (950–1150 K). The equivalence ratio was varied from 0.5 to 1.5 in 0.2 increments. Results showed that at lean equivalence ratios, low temperatures, and pressures above 60 bars, experimental IDTs could fluctuate by a factor of 100. IDTs generally decreased with increasing equivalence ratio, temperature, and pressure. These unique experimental results were then compared with IDT predictions obtained from 38 kinetic mechanisms developed for ammonia oxidation. A preliminary quantitative comparison led to the selection of 12 mechanisms. A sensitivity analysis was performed at 1050 K and an equivalence ratio of 0.7 for two different pressures (50 and 70 bars). This analysis highlighted reactions with significant impacts on ammonia IDTs, such as NH2＋NO=N2＋H2O, which inhibits reactivity, and H2NO＋O2 =HNO＋HO2 and NH2＋NO=NNH＋OH, which promote reactivity. A reaction pathway analysis indicated that HNO and OH are the most sensitive species among the six tested. According to the results, some mechanisms predict ammonia ignition well under lean conditions but not under rich conditions. Currently, no kinetic mechanism can accurately predict pure ammonia ignition under all tested conditions, particularly at high initial pressures, indicating the need for further development and refinement.