This study aims at investigating the language strengths and weaknesses of Hong Kong self-directed learners, their learning needs, and their self-directed learning experiences with the use of diagnostic language test and examining whether the test can help the learners to self-direct their own learning. The test results showed that less than half of the participants reached the satisfactory level of the diagnostic tests in the areas of listening, vocabulary, reading, and grammar, and their weakest competence was vocabulary. The findings also revealed that the learners wanted to improve their communication skills, vocabulary, as well as speaking and listening skills, and that they had a need to learn a series of specific sub-skills regarding the four areas. The results yielded that the diagnostic test provided valuable information on the self-directed language learning and suggested that teacher intervention, learning strategies, and self-evaluation skills are required for the initial development of self-directed language learning.