We　study　the　boundary　layer　problem　of　a　Keller-Segel　model　in　a　domain　of　two　space　dimensions　with　vanishing　chemical　diffusion　coefficient.　By　using　the　method　of　matched　asymptotic　expansions　of　singular　perturbation　theory,　we　construct　an　accurate　approximate　solution　which　incorporates　the　effects　of　boundary　layers　and　then　use　the　classical　energy　estimates　to　prove　the　structural　stability　of　the　approximate　solution　as　the　chemical　diffusion　coefficient　tends　to　zero.