This thesis reports a research project in the area of form focused instruction (FFI) focusing on its role and effect on one aspect of grammatical competence namely syntactic complexity development of a group of advanced ESL learners in Hong Kong. The study aims to find out (i) the syntactic complexity profile of this group of learners, (ii) the effect of FFI on the development of metalinguistic knowledge, syntactic complexity, and the acquisition of some target advanced forms, and (iii) the perception of learners of the role and effect of their FFI experience. The explicit FFI treatment involved was a 13 week long course called Structure of English offered to a group of students of Associate Degree of Translation and Interpretation of a community college in Hong Kong. Three studies were designed to collect the necessary data. Study 1 and Study 3 were questionnaire surveys to collect data regarding learners‘ perceptions of grammar learning and their grammar learning experience. Study 2, the main study, was a one group time-series quasi-experiment and data collection was done in three phases: pretest1, pretest 2 and posttest. Each test consisted of three test tasks: the term recognition task, the error correction task and the production task. ANOVA results indicate that explicit FFI has a substantial and evident effect on metalinguistic knowledge development but no significant effect on explaining errors, and on most of the syntactic complexity measures. The effect on acquisition of some target forms was differential. Perception data largely support the statistical findings and confirm a facilitating role of FFI. Perception data also reveal that grammar as a subject with contents and the preference for a transmission model were deep-seated values in learners. The implications of the findings for FFI research and syntactic development research were discussed.