We have grown undoped n-BaSi2 epitaxial films with different grain sizes on Si(111) and characterized their minority-carrier lifetime, τ. We found that τ value in undoped n-BaSi2 did not depend on average grain area, but on surface condition. The samples with mirror surfaces had large τ of about 0.4 μs and those with cloudy surface small τ of about 8 μs. We tried to cap the sample surface in situ with a 3 nm Ba or Si layer in order to control the surface of BaSi2, and succeeded to intentionally form BaSi2 with large τ.