L-type lectin receptor kinases (LecRK) are membrane-spanning receptor-like kinases with putative roles in biotic and abiotic stress responses and in plant development. In Arabidopsis, 45 LecRK were identified but their functions are largely unknown. Here, a systematic functional analysis was carried out by evaluating phenotypic changes of Arabidopsis LecRK T-DNA insertion lines in plant development and upon exposure to various external stimuli. None of the LecRK T-DNA insertion lines showed clear developmental changes, either under normal conditions or upon abiotic stress treatment. However, many of the T-DNA insertion lines showed altered resistance to Phytophthora brassicae, Phytophthora capsici, Pseudomonas syringae, or Alternaria brassicicola. One mutant defective in LecRK-V.5 expression was compromised in resistance to two Phytophthora spp. but showed enhanced resistance to Pseudomonas syringae. LecRK-V.5 overexpression confirmed its dual role in resistance and susceptibility depending on the pathogen. Combined analysis of these phenotypic data and LecRK expression profiles retrieved from public datasets revealed that LecRK which are hardly induced upon infection or even suppressed are also involved in pathogen resistance. Computed coexpression analysis revealed that LecRK with similar function displayed diverse expression patterns. Because LecRK are widespread in plants, the results presented here provide invaluable information for exploring the potential of LecRK as novel sources of resistance in crops.