We report 48 % efficient single-pass second harmonic generation of high-power ultrashort-pulse ( $${\approx }250\,{\rm fs}$$ ≈ 250 fs ) Yb-fiber laser by utilizing type-I phase matching in $${\rm LiB}_3{\rm O}_5$$ LiB 3 O 5 (LBO) crystal. The choice of LBO among other borate crystals for high-power frequency doubling is essentially motivated by large thermal conductivity, low birefringence and weak group velocity dispersion. By optimally focussing the beam in a 4-mm-long LBO crystal, we have generated about 2.3 W of average power at 532 nm using 4.8 W of available pump power at 1064 nm. The ultrashort green pulses were found out to be near-transform limited $${\rm sech}^2$$ sech 2 pulses with a pulse width of $$\Delta \tau \approx 150\,{\rm fs}$$ Δ τ ≈ 150 fs and being delivered at 78 MHz repetition rate. Due to appreciably low spatial walk-off angle for LBO ( $${\approx }0.4^{\circ }$$ ≈ 0 . 4 ∘ ), we obtain $$M^2<1.26$$ M 2 < 1.26 for the SH beam which signifies marginal distortion in comparison with the pump beam ( $$M^2<1.15$$ M 2 < 1.15 ). We also discuss the impact of third-order optical nonlinearity of the LBO crystal on the generated ultrashort SH pulses.