The present invention relates to a filter cap for a syringe, and, more specifically, to one comprising: a housing having a through-passing injection-liquid inflow passage, a syringe needle insertion passage that passes through so as to link through to the injection-liquid inflow passage in such a way that a syringe needle can be inserted therein, and an injection needle tight-fitting passage that passes through so as to link through to the syringe needle insertion passage in such a way that it is possible to tightly fit the syringe needle therein and form a negative pressure; and a filter which is fitted by melt adhesion to a through-linking portion of the injection-liquid inflow passage and the syringe needle insertion passage in such a way that it is possible to filter the injection liquid.