A frequency tunable external-cavity diode laser (ECDL) using a narrow bandwidth (∼0.3 nm) interference filter has been developed for resonance ionization spectroscopy of strontium (Sr) with high isotopic selectivity. Improved wavelength and single mode stabilities of this interference-filter-type ECDL (IF-ECDL) over a commonly used (also home-made) Littrow-type ECDL were theoretically expected and experimentally confirmed by both a wavelength meter and a home-made Fabry-Perot interferometer. The measured spectral profile of the dominant isotope 88Sr using our IF-ECDL in the 689.4 nm intercombination transition shows that the Lorentzian component (∼1.3 MHz) of the spectrum width is consistent with the obtained fringe width of the interferometer. High 90Sr isotopic selectivity of ∼104 with respect to 88Sr is expected in this transition, which indicates that even if the manufacturing accuracy is not comparable to commercial Littrow-type ECDLs, our compact IF-ECDL having sufficient wavelength stability is a promising laser source for background-free analysis of radioactive 90Sr in marine samples.